Are the sum of 2 prime numbers prime or composite?

1.

$2x + 3y - x + 2y$

Group like terms:
$(2x - x) + (3y + 2y)$

Combine $x$ terms:
$2x - x = 1x = x$

Combine $y$ terms:
$3y + 2y = 5y$

Simplified expression:
$x + 5y$

$\boxed{x + 5y}$

2.

$4a - 3b + 2a - b$

Group like terms:
$(4a + 2a) + (-3b - b)$

Combine $a$ terms:
$4a + 2a = 6a$

Combine $b$ terms:
$-3b - b = -4b$

Simplified expression:
$6a - 4b$

$\boxed{6a - 4b}$

3.

$5p + 2q - 3p + q$

Group like terms:
$(5p - 3p) + (2q + q)$

Combine $p$ terms:
$5p - 3p = 2p$

Combine $q$ terms:
$2q + q = 3q$

Simplified expression:
$2p + 3q$

$\boxed{2p + 3q}$

4.

$3m + 2n - m - n$

Group like terms:
$(3m - m) + (2n - n)$

Combine $m$ terms:
$3m - m = 2m$

Combine $n$ terms:
$2n - n = 1n = n$

Simplified expression:
$2m + n$

$\boxed{2m + n}$