if y=5x-2, then -3x=? PLEASE EXPLAIN

a 5x -6
b 15x-6
c 15x+6
d -15-6
e -15x+6

if y = 5x -2 then

5x=y+2 and
x = (y+2)/5, then
3x = 3(y+2)/5 and
-3x = -3(y+2)/5 which unfortunately is not one of your answers.

Did you make a typo?
did you mean find -3y ???
then it is even easier, just follow my steps.