I cannot help you unless I know what ones you need help on
A all squares have the sides
It depends on which variable is eliminated.
If you multiply the second equation by -1 and eliminate the y:
3x - y = 7
-6x + y = -10
-3x = -3 or x = 1
If you multiply the first equation by -2 and eliminate the x:
-6x + 2y = -14
6x - y = 10
y = -4
From the recursive rule

it follows that


and so on. Notice how the subscript on a on the right side and the coefficient multiplied by 13 add up to n (n - 2 + 2 = n; n - 3 + 3 = n; and so on). If we continue the pattern, we'll end up with

so that the explicit rule for the n-th term in the sequence is
