It sounds like you're given
[tex]8^y = 16^{y+2}[/tex]
and are asked to solve for y.
Notice that 8 = 2³ and 16 = 2⁴, so you can rewrite both sides with a common base:
[tex]8^y = 16^{y+2} \\\\ (2^3)^y = (2^4)^{y+2} \\\\ 2^{3y} = 2^{4(y+2)} = 2^{4y+8}[/tex]
The bases match, so the exponents must be equal:
3y = 4y + 8
Solve for y :
3y - 4y = 8
-y = 8
y = -8
