45 ÷ 3 = 15 R0
Alright, let's work through the division of 45 by 3 step by step.

Step 1:
3 goes into 4 1 times with a remainder of 1.
Write down 1 as next digit of of the result. 
Result so far: 1
Subtract 3 from 4 to get 1.
Bring next digit (5) of the dividend behind the 1 and repeat the process: 15 / 3

Step 2:
3 goes into 15 5 times with a remainder of 0.
Write down 5 as next digit of of the result. 
Result so far: 15
Subtract 15 from 15 to get 0.

The final result is 15 with a remainder of 0.