To find out how many passes the quarterback will attempt if he completes 15 passes, we can first determine his completion rate based on his performance in the last game.
He completed 10 out of 18 passes, which gives us a completion rate of:
\[ \text{Completion Rate} = \frac{10}{18} = \frac{5}{9} \]
Now, we want to find the number of attempts \( x \) when he completes 15 passes. Using the completion rate we calculated:
\[ \frac{5}{9} = \frac{15}{x} \]
We can cross-multiply to solve for \( x \):
\[ 5x = 9 \cdot 15 \]
Calculating \( 9 \cdot 15 \):
\[ 9 \cdot 15 = 135 \]
So we have:
\[ 5x = 135 \]
Now, divide both sides by 5:
\[ x = \frac{135}{5} = 27 \]
Thus, if the quarterback completes 15 passes, he will attempt 27 passes.