Sure thing, let's get straight to it. We start with 90 and we're going to multiply it by 5, which means adding 90 to itself 5 times.
Step 1: 0 + 90 = 90
Step 2: 90 + 90 = 180
Step 3: 180 + 90 = 270
Step 4: 270 + 90 = 360
Step 5: 360 + 90 = 450

So, 90*5 = 450