percent means parts ouf of 100 so
x%=x/100
40%=40/100=0.4
'of' means multipy
therefor
40% of 85=0.4 times 85=34
25% of 64 =0.25 times 64=16
10% of 150 =0.1 times 150=15
70% of 30 =0.7 times 3=21
50% of 400=0.5 times 400=200
15% of 200 =0.15 times 200=30