Alright, let's work through 3501 times 210 step by step
3501 × 210 = 210 × (3501)
+ 210 × 1 yielding 210
+ 210 × 00 which equals 0
+ 210 × 500 that is equal 105000
+ 210 × 3000 that is equal 630000

= 735210
