20x - 18 < 50 < 36x - 16

So this is actually composed o 2 sentances

20x-18<50 AND 50<36x-16

so solve each and find solutions where x is the same in both sentances

20x-18<50

add 18 to both sides

20x<68

divide both sides by 20

x<3 and 2/5

then the second sentance

50<36x-16

add 16 to both sides

66<36x

divide both sides by 36

1 and 5/6
so

since it is and, combine

3 and 2/5>x>1 and 5/6 or

17/5>x>11/6

the solution is

S=x