*MATH HELP* how exactly do you do the work for finding the missing terms in a arithetic sequence

question is:
5,____,____,____,-7

and another thing i need help with is
___,8____,____,44

so I just need to know like what forumla or how you would work out to find the missing numbers... weather you have the first and last or a random number in the middle and last etc. :)
Thanks if you could help explain!
I believe it has to do something with this forumla:
a↓n =dn+c

the "n" goes underneath the a like a exponent underneath.

An arithmetic sequence always go up or down by the same number d called common difference.
example; take the sequence 2, 5, 8, 11......
this has 1st term 2 and common difference 3
take the sequence 25, 23, 21, 19.....
this has 1st term 25 and common difference -2
In general an arithmetic sequence can be written a, a+d, a+2d, a+3d .....
this has 1st term a and common difference d, second term a+1d, 3rd term a+2d and so on.

5,----, ------, -----, -7 here 1st term is 5 and 5th term is -7.
ie a=5 and a+4d=-7 ie 5+4d = -7 so 4d =-12 giving d =-3 so missing terms are 2, -1, -4.

...., 8, ..., ....., 44 here 2nd term is 8 and 5th term is 44
ie a+d=8 and a+4d =44 ie a+d+3d =44 so 8+3d=44 giving d=12 and a=8-12=-4
this sequence goes, -4, 8, 20, 32, 44