Explain how am estimate you to place the decimal point when multipling 3.7 x 5.1

Since 3*5=15, then the answer to 3.7*5.1 should be close to that same value. But if you were solving it by hand, and accidentally wrote the answer as 1.887 or 188.7. Estimating helps you know that you placed the decimal in the wrong area, Since the number isn't close to 15.3.7*5.1+18.87

Well 3.7×5.1 put the decimals at the end so 37×51=1887 there is 2 decimals so it should be 18.87 you put it back 2 spaces since there's 2 decimals