To decrease this amount by 15% we must first find out what is 15% percent.
We can do that by multiplying the decimal of 15% by 120
15% = 0.15
0.15 x 120 = 18
So 18 is 15% of 120.
Wait! that's not the answer. We are asked to decrease by 15%
So 120 - 18 = 102
Your answer is £102