일차방정식

Since the product of a number and its reciprocal is 1, our strategy will be to isolate $x$ by multiplying by the reciprocal of $\frac{3}{4}$.

Multiply by the reciprocal of $\frac{3}{4}$.
Reciprocals multiply to 1.
Multiply.
Notice that we could have divided both sides of the equation $\frac{3}{4}x=12$ by $\frac{3}{4}$ to isolate $x$. While this would work, most people would find multiplying by the reciprocal easier.
Check:
Substitute $x=16$.