3 over 12 equal 5 over x
3/12=5/x
Multiply each denominator by the the numerator of the other fraction.
12*5=60
3*x=3x
Set them equal to each other.
60=3x
Divide by 3 to leave only x.
x=20
\(\begin{array}{rll}\dfrac{3}{12}&=&\dfrac{5}{x}\\\dfrac{1}{4}&=&\dfrac{5}{x}\\\dfrac{5}{20}&=&\dfrac{5}{x}\\x&=&20\end{array}\)
Same as Mellie's answer, only difference is the steps.
