Let \( x \) be the number of grapes Takehiko brought to school. According to the problem, he gave away 15 grapes and is left with 45 grapes. We can express this with the following equation:
\[ x - 15 = 45 \]
To find \( x \), we can add 15 to both sides of the equation:
\[ x = 45 + 15 \] \[ x = 60 \]
Takehiko brought 60 grapes to school.
So the answer is \( \boxed{60} \).