Answer
$\dfrac{ 9 }{ 10 }$
Work Step by Step
To combine fractions, make sure that the fractions have the same denominators before combining their numerators.
\begin{align}
\dfrac{ 3 }{ 4 } + \dfrac{ 3 }{ 20 } &= \dfrac{ 15 }{ 20 } + \dfrac{ 3 }{ 20 } &&\text{Make equivalent fractions} \\
&= \dfrac{ 15 + 3 }{ 20 } &&\text{Add the numerators} \\
&= \dfrac{ 18 }{ 20 } \\
&= \dfrac{ 18 \div 2 }{ 20 \div 2 } &&\text{Reduce to lowest terms} \\
&= \boxed{ \dfrac{9}{10} }
\end{align}
