GMAT Quantitative Reasoning Practice Test 1

Let $\mathit{x}=$ the number of liters of the $40\%$ solution. Use the equation $0.40\mathit{x}+0.20\left(35\right)=0.35\left(\mathit{x}+35\right)$ to show the two amounts mixed equal the $35\%$ solution.
Solve the equation: $0.40\mathit{x}+0.20\left(35\right)=0.35\left(\mathit{x}+35\right)$
Multiply both sides by 100 in order to work with more compatible numbers:
$40\mathit{x}+20\left(35\right)=35\left(\mathit{x}+35\right)$
$40\mathit{x}+700=35\mathit{x}+1,225$
Subtract 700 on both sides: $40\mathit{x}+700-700=35\mathit{x}+1,225-700$
Subtract $35\mathit{x}$ from both sides $40\mathit{x}-35\mathit{x}=35\mathit{x}-35\mathit{x}+525$
Divide both sides by 5 :
$5\mathit{x}/5=525/5\mathit{x}=105$ liters of $35\%$
iodine solution