SAT Mathematics Practice Test 3

First, clear the fractions from the given equation by multiplying each side of the equation by 36 (the least common multiple of 4,9, and 12).
The equation becomes $28\mathit{x}-16\mathit{x}=9+15.$
Combining like terms on each side of the equation yields $12\mathit{x}=24$.
Finally, dividing both sides of the equation by 12 yields $\mathit{x}=2$.
Alternatively, since$\frac{7}{9}\mathit{x}-\frac{4}{9}\mathit{x}=\frac{3}{9}\mathit{x}=\frac{1}{3}\mathit{x}$ and $\frac{1}{4}+\frac{5}{12}=\frac{3}{12}=\frac{8}{12}=\frac{2}{3}$ the given equation simplifies to $\frac{1}{3}\mathit{x}=\frac{2}{3}$.
Multiplying of $\frac{1}{3}\mathit{x}=\frac{2}{3}$ by 3 yields $\mathit{x}=2$