Question 643377
what is {{{a + b}}}?

Whenever you multiply two terms with the same base, you can add the exponents:

        {{{( x^ m )( x^ n ) = x^( m + n )}}}

so, you have:

{{{(y^2) *(y^a) = y^8}}} ...=>...if bases are equal, then exponents are equal too

{{{y^(2+a) = y^8}}}...=>...{{{2+a=8}}}=>...{{{a=8-2}}}=>...{{{highlight(a=6)}}}

and 

-Whenever you have an exponent expression that is raised to a power, you can multiply the exponent and power:

        {{{( x^m )^n = x^( m n)}}}

so, you have:

{{{(y^2)^b= y^12}}} ...=>...{{{(y^(2b))= y^12}}}...=>...{{{2b= 12}}}...=>...{{{highlight(b= 6)}}}

{{{a + b=6+6=12}}}