Everywhere you see z, replace the letter with 18.
z/[(3- 2z)] + 4(z - 8)
18/[(3 - 2(18))] + 4(18 - 8)
You finish.
0.15x + x <(or equal to) 50
Where x is the meal's cost (no tip included)
50 - 15% = 42.5.
x >(or equal to) 42.50.
(nothing is copied content, I copy pasted a number into the right position, feel free to check it mods)