You need to use the distributive property a(b + c) = ab + ac
and vice versa ab + ac = a(b + c)
Let's do the first expression
7r + 8r + 2
As you can see in first two terms r is common so take out common
r(7 + 8) + 2
The other way of doing it is you can take the GCF of both terms.
For second expression 3a + 6b
GCF of 3a and 6b is 3
so, take that out and rewrite the expression as 3(a + 2b)
Try doing other expressions and if you're still not able to work myself or any other tutor will be glad to help you.