$$ (4-\frac{9}{2})^2 = \left( 4-\frac{ 9 }{ 2 } \right) \cdot \left( 4-\frac{ 9 }{ 2 } \right) = 16-18-18 + \frac{ 81 }{ 4 } $$

Combine like terms

Multiply $qrst$ by $ \dfrac{1}{4} $ to get $ \dfrac{ qrst }{ 4 } $.

Step 1: Write $ qrst $ as a fraction by putting $ \color{red}{1} $ in the denominator.

Step 2: Multiply numerators and denominators.

Step 3: Simplify numerator and denominator.

$$ \begin{aligned} qrst \cdot \frac{1}{4} & \xlongequal{\text{Step 1}} \frac{qrst}{\color{red}{1}} \cdot \frac{1}{4} \xlongequal{\text{Step 2}} \frac{ qrst \cdot 1 }{ 1 \cdot 4 } = \\[1ex] & \xlongequal{\text{Step 3}} \frac{ qrst }{ 4 } \end{aligned} $$

Add $ \dfrac{qrst}{4} $ and $ \dfrac{9}{2} $ to get $ \dfrac{ \color{purple}{ qrst+18 } }{ 4 }$.

To add raitonal expressions, both fractions must have the same denominator.
We can create a common denominator by multiplying the second fraction by $\color{blue}{2}$.

$$ \begin{aligned} \frac{qrst}{4} + \frac{9}{2} & = \frac{ qrst }{ 4 } + \frac{ 9 \cdot \color{blue}{ 2 }}{ 2 \cdot \color{blue}{ 2 }} = \\[1ex] &=\frac{ \color{purple}{ qrst } }{ 4 } + \frac{ \color{purple}{ 18 } }{ 4 }=\frac{ \color{purple}{ qrst+18 } }{ 4 } \end{aligned} $$