Alright, let's work through 78971121 times 78137521 step by step
78971121 × 78137521 = 78137521 × (78971121)
+ 78137521 × 1 that is equal 78137521
+ 78137521 × 20 that equals 1562750420
+ 78137521 × 100 what gives us 7813752100
+ 78137521 × 1000 yielding 78137521000
+ 78137521 × 70000 that is equal 5469626470000
+ 78137521 × 900000 giving us 70323768900000
+ 78137521 × 8000000 producing 625100168000000
+ 78137521 × 70000000 resulting in 5469626470000000

= 6170607625531041
