remember, we can add like terms
also remember the commutative property of addition which is
you can move the order around when adding or a+b=b+a
also, distributive property which is a(b+c)=ab+ac
so
distribute first
7(B+3)=7(B)+7(3)=7B+21
now we have
7B+21+2B
by the commutative property
7B+2B+21
adding like terms
9B+21
answer is 9B+21
