is means equal in mathematics
of means multiplication
and if we are solving for x then we can translate your equation to:
[tex]\sf{x=\frac{1}{4}\times\frac{1}{12}}[/tex]
Simplifying that more, we get:
[tex]\sf{x=\frac{1}{48}}[/tex]
And your final answer is:
[tex]\huge{\boxed{\bf{\frac{1}{48}~is~\frac{1}{4}~of~\frac{1}{12}}}}[/tex]
