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

Okay this is how i did it,  6(31) + 6(4)  -  6(15)  186  +  24   -  90         = 120