Alright, let's work through 1648 times 2580 step by step
1648 × 2580 = 2580 × (1648)
+ 2580 × 8 giving us 20640
+ 2580 × 40 what gives us 103200
+ 2580 × 600 that is equal 1548000
+ 2580 × 1000 that is equal 2580000

= 4251840
