Hi there!
The replacement set is the set of values that may be subtituted for the variable. To find the solution set from the replacement set, you need to plug in each value frome the replacement set and evaluate both sides of the equation. If the two sides are equal, the equation is true and the value is a solution.
Here are the steps into solving this problem :
Try 1 :
7(0) - 3 = 18 ?
0 - 3 = 18 ?
-3 ≠ 18
Try 2 :
7(2) - 3 = 18 ?
14 - 3 = 18 ?
11 ≠ 18
Try 3 :
7(3) - 3 = 18 ?
21 - 3 = 18 ?
18 = 18
Try 4 :
7(4) - 3 = 18 ?
28 - 3 = 18 ?
25 ≠ 18
Your answer is : x = 3
There you go! I really hope this helped, if there's anything just let me know! :)