Use properties of operations to write an expression equivalent to the sum of the expressions 3(g + 5) and 2(3g - 6)

Well,  you would istribute
using
a(b+c)=ab+ac
so

3(g+5)=3(g)+3(5)=3g+15
2(3g-6)=2(3g)+2(-6)=6g-12

now we gots
3g+15+6g-12
using commutative, we can arrange and group like terms because
a+b=b+a
so
3g+6g+15-12
add
9g+3

Lie