What's an equivalent expression for 7(2x + 9)

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