[tex]\frac{5}{30} =\frac{x}{90}[/tex]
Match the denominators:
[tex]\frac{5}{30} *\frac{3}{3}= \frac{15}{90}[/tex]
x = 15
Check your work:
[tex]\frac{15}{90} \div \frac{3}{3} = \frac{5}{30}[/tex]
We know that x = 15