apply the definition of sustraction in fractions
[tex]\frac{a}{b}-\frac{c}{d}=\frac{ad-bc}{bd}[/tex]using this apply the definition
[tex]\begin{gathered} \frac{1\cdot8-4\cdot1}{8\cdot4} \\ \frac{8-4}{32} \\ \frac{4}{32} \end{gathered}[/tex]simplify the expression by dividing both numerator and denominator by 4
[tex]\frac{1}{8}[/tex]