Let's first split this expression into two parts. We have the (2h)7 and 7h. We need to simplify the (2h)7 before we can combine them.
(2h)7 = 27*h7=128*h7=128h7. In this step the exponent can be distrubed into the parenthese to each individual term.
We can now combine the 7h with what we got in the previous step:
128h7*7h=128*7*h7*h=896h8. As per law of exponents: xm*xn=xm+n.
Hope this helps.