Question

What is the value of x?

Answer 1

$\left\{\begin{array}{ccc}x+2y=4&\text{multiply both sides by 5}\\4x-5y=42&\text{multiply both sides by 2}\end{array}\right\\\\\underline{+\left\{\begin{array}{ccc}5x+10y=20\\8x-10y=84\end{array}\right}\qquad\text{add both sides of the equations}\\.\qquad13x=104\qquad\text{divide both sides by 13}\\\\\boxed{x=8}\\\\Answer:\ \boxed{\boxed{x=8}}$