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0.15x+0.4(50-x)=15
We move all terms to the left:
0.15x+0.4(50-x)-(15)=0
We add all the numbers together, and all the variables
0.15x+0.4(-1x+50)-15=0
We multiply parentheses
0.15x-0.4x+20-15=0
We add all the numbers together, and all the variables
-0.25x+5=0
We move all terms containing x to the left, all other terms to the right
-0.25x=-5
x=-5/-0.25
x=+20
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