It's a simple linear equation in 'n'. There's only one number that 'n' can be
that will make the equation a true statement. That number is called the
'solution' to the equation. Here's one way to find it:
You said that -7n - 4 = 24
Add 4 to each side: -7n = 28
Multiply each side by -1 : 7n = -28
Divide each side by 7 : n = -4
Homework is the only way for most people to learn stuff.