No problem, we've got 1639 and 4375 to multiply
1639 × 4375 = 4375 × (1639)
+ 4375 × 9 what gives us 39375
+ 4375 × 30 yielding 131250
+ 4375 × 600 that equals 2625000
+ 4375 × 1000 giving us 4375000

= 7170625
