Let's roll up our sleeves and solve this. We have 303 and we're going to multiply it by 7, essentially adding 303 to itself 7 times.
Step 1: 0 + 303 = 303
Step 2: 303 + 303 = 606
Step 3: 606 + 303 = 909
Step 4: 909 + 303 = 1212
Step 5: 1212 + 303 = 1515
Step 6: 1515 + 303 = 1818
Step 7: 1818 + 303 = 2121

So, 303*7 = 2121