Question 187121
x*2x/(x+2x)=40
2x^2/3x=40
2x^2=3x*40
2x^2=120x
2x^2-120x=0
2x(x-60)=0
2x=0 
x=0/2
x=0 ans.
x-60=0
x=60 ans.
Proof:
60*120/(60+120)=40
7200/180=40
40=40