No problem, we've got 1644 and 7847 to multiply
1644 × 7847 = 7847 × (1644)
+ 7847 × 4 that equals 31388
+ 7847 × 40 that equals 313880
+ 7847 × 600 giving us 4708200
+ 7847 × 1000 producing 7847000

= 12900468
