Is there anyone good at maths

because i'm hopless at maths i can't figure this qs out and i looked at the qs at first and thought it was impossible to solve:

Mum, Dad and their two children arrive at the river where is a boat that will hold one adult or two children. what is the minimum number trips across the river in either direction to the family across?
a. 7
b. 9
c.11
d. 13
e. 15

the answers is 9 but i don't know why and it seems impossible to get that answer
could anyone help me and explain it?

Is a additional sailor is there ?
can a child sail a boat ?

if child ca sail and additional sailor is not there then
Trip 1 --------> 2 children
Trip 2 <--------- 1 child return
Trip 3 --------> father crosses
Trip 4 <--------- 2nd child return
Trip 5 ----------> again 2 children
Trip 6 <---------- 1 child return
Trip 7 ----------> mother crosses
Trip 8 <--------- 2nd child return
Trip 9 --------> 2 children crosses
------

First trip - First two children go across
Second trip - one child brings the boat back- one child is left at the other bank
Third trip - Dad goes in the boat. Dad and one child reach the other bank
Fourth trip - other child brings the boat back -Dad is left at the other bank
Fifth trip - both children go across - 2 children and Dad have crossed
Sixth trip - one child brings the boat back- Dad and one child are left at the other bank
Seventh trip - Mom goes across - Dad, Mom and 1 child have crossed
Eight trip -other child brings the boat back - Dad and Mom have crossed the river
Ninth trip - Both the children go across -Mom Dad and both children have crossed the river

Trip #1: both kids row there
#2: 1 kid comes back
#3: Dad goes
#4: other kid rows back
#5: both kids go there again
#6: one of the kids rows back
#7: mom goes
#8: kid still there rows back
#9: both kids row there
(By there, I mean the destination)

M,D,C1 C2
(1) let boat C1C2------------------------------> C1C2
(2) C1 boat<-----------------------------------…
(3) M boat---------------------------------> M
(4) C2 boat<-----------------------------------…
(5) C1C2boat--------------------------------…
(6) C2boat ------------------------------------- >MC1
(7) Dboat-----------------------------------… MDC1
(8) C1boat <---------------------------------------… MD
(9) C1C2 boat------------------------------------… MD C1C2
explanation--[1.c1c2 took boat,(2) c1 came back (3) mum took boat (4)c2 came back
(5) c1c2 took boat (6)c1 came back ( 7)Dad took boat (8) c2 came back(9) bothc1 c2 took boat.

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