What number is 5% of 45?explain it well.. i don't understand things as much

2.25
45/x=100/5
(45/x)*x=(100/5)*x       - we multiply both sides of the equation by x
45=20*x       - we divide both sides of the equation by (20) to get x
45/20=x 
2.25=x 
x=2.25

Always the % number is have to be over 100 5/100=5%
ex. 39%=39/100

45 we do not know what is it so we put (y) 45/y or any other letter 

now we put them together
5/100=45/y
we solve for y
5y=100x45
5y=4500 divide  by 5
y=900
That is the answer I hope it is helpful

m:n=2:1