Let's calculate 1987 x 3680
1987 × 3680 = 3680 × (1987)
+ 3680 × 7 that results in 25760
+ 3680 × 80 that results in 294400
+ 3680 × 900 which equals 3312000
+ 3680 × 1000 that equals 3680000

= 7312160
