Find the product.

(y 3) 2 · y 7

If you expand the parentheses this it can be written as

(y*y*y) (y*y*y) * y^7

This shows since they are all being multiplied that you can add the exponents when they are expanded and still equal the same ... this is the same as multiplying the 3 and 2 exponents together in the original problem

y^6*y^7 do the same to these exponents add them together

y^13

If you mean:

(y^3) ^2*y^7

rule (a^b) ^c=a^ (b*c)

y^6*y^7

rule a^b*a^c=a^ (b+c)

y^13