Let's simplify the expression step by step:

$(21 - 2x) - (5 - 4x)$

1. Distribute the negative sign to the second parentheses:

$21 - 2x - 5 + 4x$

2. Combine like terms:
   • Constant terms: $21 - 5 = 16$
   • $x$-terms: $-2x + 4x = 2x$

So the simplified expression is:

$16 + 2x$

Let me know if you'd like further clarification or have more questions!

Related questions:

1. How do you factor the expression $16 + 2x$?
2. What happens if you set $16 + 2x = 0$ and solve for $x$?
3. How would you solve an equation like $(5 - 3x) - (7 - 2x)$?
4. How can you graph the expression $16 + 2x$?
5. How do you solve a system of equations involving linear expressions?

Tip:

When simplifying expressions with parentheses, always distribute the signs first and then combine like terms for clarity!