Antonio has a change jar that contains $3.65 in half dollars and nickels. He has 7 more nickels than half dollars. How many of each type of coin does he have?

Let h be half dollars
Let n be nickels

We're given two equations:

n = h + 7

0.5h + 0.05n = 3.65

Substitute equation (1) into equation (2) for n:
0.5h + 0.05(h + 7) = 3.65