an equivalent expression means that we need an equation that is equal to the one you have listed
one way you can do this is to multiply the 7 by each term in the parentheses
this will give us 14x + 63
Here is how we check if these are equivalent. pick a number to replace "x" and then solve the problem. if we get the same answer from both expressions then we are correct
Im going to choose the number 1
7(2(1) + 9)
7(2+9)
7(11)
77
now replace "x" with the number 1 in our new expression and if we get 77 then they are equivalent
14x+63
14(1)+63
14+63
77
so 14x+63 is an equivalent expression