#### Answer

$27$

#### Work Step by Step

We start with the given expression: $45-18$
First, we will convert this to an addition problem: $45+(-18)$
We can find the sum of a positive and a negative integer by subtracting the smaller absolute value from the larger absolute value and giving the result the sign of the original number that has the larger absolute value.
Since $|45|>|-18|$, we can subtract $18$ from $45$, giving us $27$. Since the larger absolute value was originally positive, the result is positive: $27$