So Cruz has d amount of 10$ bills.
The value of this money is 10d in dollars.
He has 3 fewer than d amount of 20$ bills.
So he has (d-3) of these 20$ bills.
The value of this money is 20(d-3) in dollars.
The total money that Cruz has is the sum of these values that we've already calculated:
10d + 20(d-3)
From there, you'll need to distribute the 20 to each term in the second set of brackets, and then combine like-terms to simplify.
