Question

Can someone please answer these questions?

Answer 1

Keep in mind that you can gather only like terms. Two terms can be summed/subtracted if they involve the same powers of the same variables.

So, going point by point:

1. We can subtract the terms, because they both involve the variable $b$, and we have $3b-7b = (3-7)b = -4b$
2. We can sum the terms, because they all involve the variable $a$, and we have $a+a-5a = (1+1-5)a = -3a$
3. We can't sum this terms: 3 is a pure number, while 3r involves the variable r.
4. We can only sum the two terms: we have $7t-8t-8 = (7-8)t-8 = -t-8$
5. We can't sum this terms: -20 is a pure number, while -15p involves the variable p.
6. We can sum the terms, because they all involve the variable $g$, and we have $-g-g-g = (-1-1-1)g = -3g$