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, what is the perimeter of polygon $PQRST$? [asy]

import olympiad;

size(6cm); // ADJUST

pair p = (0, 6);
pair q = (3, 6);

pair r = (3, 3);
pair t = (0, 0);
pair s = (7, 0);

draw(p--q--r--s--t--cycle);
label("$P$", p, NW);
label("$Q$", q, NE);
label("$R$", r, E + NE);
label("$S$", s, SE);
label("$T$", t, SW);

label("$6$", p / 2, W);
label("$3$", p + (q - p) / 2, 2 * N);
label("$7$", s / 2, S);

draw(rightanglemark(p, t, s));
draw(rightanglemark(t, p, q));
draw(rightanglemark(p, q, r));
add(pathticks(p--q, s=6));
add(pathticks(q--r, s=6));
[/asy]
user