15% of x = 21
Set up proportions.
15/100 = 21/x
Cross multiply the numbers (15 by x, 21 by 100).
Divide 2100 by 15x to get x.
2100/15 = 140
X is 140.
2x-9 =6
2x= 15
x= 7.5
I think thats the answer.
M-30=10
It could also be 30-m=10
The answer for the first one would be 10+30=m
m=40
The answer for the second one would be 30-10=m
m=20
Hope this helps :)