SOLUTION: what is the 10th,20th,and 30th terms of 1.)3,14,25,36,47 2.)25,38,51,64,77

I'll just find the 10th term of 1.)  The others are done the same way.

Use the formula

an = a1 + (n-1)·d

You have a1 = 3, and n = 10. But you also need d.

To find d you subtract the 1st term from the 2nd term:

d = a2 - a1 = 14 - 3 = 11

But you should also check to make sure that the sequence is arithmetic,
otherwise the formula would not work:

d = a3 - a2 = 25 - 14 = 11
d = a4 - a3 = 36 - 25 = 11
d = a5 - a4 = 47 - 36 = 11

If any of those had been different, the above formula would not work.
But since they're all the same it will work.

For the 10th term, 

an = a1 + (n-1)·d
a10 = 3 + (10-1)·11
an = 3 + (9)·11
an = 3 + 99
an = 102

You can find all the others exactly the same way.

Edwin