To determine how much money, \( d \), Matt has given that Graham has $45 and he has 5 times as many dollars as Matt, we can use the relationship:
\[ 45 = 5 \times d \]
This means Graham's money ($45) is equal to 5 times Matt's money (\( d \)).
So the correct equation that could be used to determine how much money Matt has is:
45 = 5 x d.