(40-x)/(50+x)=50%
(40-x)/(50+x)=0.5
40-x=0.5(50+x)
40-x=25+0.5x
0.5x+x=40-25
1.5x=15
x=15/1.5
x=10
(40-x)/(50+x)=50%
40-x=25+50%x
-x-50%x=25-40
-1.5x=-15
x=10
(40-x)/(50+x)=50%
2*(40-X)=(50+X)*1
80-2X=50+X
3X=30
X=10
(40-x)/(50+x)=50%
40-x=50%(50+x)
40-x=25+0.5x
1.5x=15
x=10