Easy math questions plz

Hi,

1) the sum of the digits of a certain two-digit number is 7. Reversing its digits increase the number by 9.
What is the number?

T + U = 7
10U + T - (10T + U) = 9

T + U = 7
10U + T - 10T - U = 9

T + U = 7
9U - 9T = 9

T + U = 7
U - T = 1
---------------
2U = 8
U = 4
T = 3

The number is 34. <==ANSWER

2) a boat traveled 210 miles downstream and back. The trip downstream took 10 hours. The trip back took 70 hours. What is the speed of the boat in still water? What is the speed of the current?

10(x + y) = 210
70(x - y) = 210

10x + 10y = 210
70x - 70y = 210

7(10x + 10y = 210)
70x - 70y = 210

70x + 70y = 1470
70x - 70y = 210
-----------------------------
140x = 1680

x = 12

If x = 12 and x + y = 21, then y = 9

The boat went 12 mph and the rate of the river was 9 moh. <==ANSWER

3)The state fair is a popular field trip destination. This year the senior class at highschool A and the senior class at highschool B both planned trips there. The senior class at highschool A rented and filled 8 vans and 8 buses with 240 students. highschool B rented and filled 4 vans and 1 bus with 54 students. Every van had the same number of students in it as did the buses. Find the number of students in each van and in each bus.