Alright, let's work through 3661 times 3158 step by step
3661 × 3158 = 3158 × (3661)
+ 3158 × 1 that is equal 3158
+ 3158 × 60 what gives us 189480
+ 3158 × 600 that equals 1894800
+ 3158 × 3000 that is equal 9474000

= 11561438
