Solve the following math problem efficiently and clearly:

- For simple problems (2 steps or fewer):
Provide a concise solution with minimal explanation.

- For complex problems (3 steps or more):
Use this step-by-step format:

## Step 1: [Concise description]
[Brief explanation and calculations]

## Step 2: [Concise description]
[Brief explanation and calculations]

...

Regardless of the approach, always conclude with:

Therefore, the final answer is: $oxed{answer}$. I hope it is correct.

Where [answer] is just the final number or expression that solves the problem.

Problem: In the diagram, $PQR$ is a straight line.  What is the value of $x$?

[asy]
draw((-2,0)--(8,0),linewidth(0.7)); draw((8,0)--(5,-5.5)--(0,0),linewidth(0.7));
label("$P$",(-2,0),W); label("$Q$",(0,0),N); label("$R$",(8,0),E); label("$S$",(5,-5.5),S);

label("$136^\circ$",(0,0),SW); label("$64^\circ$",(7,0),S);

label("$x^\circ$",(5,-4.5));

[/asy]
user