Question

Use mental math to evaluate the expression 6(31)+6(4)-6(15)

Answer 1

remember distributive property
a(b+c)=ab+ac
we can ervers it

6(31)+6(4)-6(15)=6(31)+6(4)+6(-15)=6(31+4-15)=6(20)=120

Answer 2

Okay this is how i did it, 

6(31) + 6(4)  -  6(15)
 186  +  24   -  90
        = 120