Answer:
If we look at the inequality, we can see the "<" is being used.
By looking at the answer choices, we can already exclude answer options A and D because they are using the inverse symbol of the symbol being used in this inequality which is ">" not "<".
Let's solve;
42 - 3x < - 15
In every inequality, we first need to get rid of the constants.
The inverse operation of addition is subtraction (because 42 is positive).
-42 -42
-3x < -57
Now, all we need to do is isolate x by getting rid of it's coefficient.
In order to do that, we must perform the inverse operation of multiplication which is division (because -3 is being multiplied by x).
÷-3 ÷-3
x < 19, your only choice left is C.