Solve using the substitution method. Show your work. If the system has no solution or an infinite number of solutions, state this.

3x – 15y = -12
3x + 24y = -12

Rather than substitution, why don't we just subtract them as they stand.

-29y = 0
y = 0
then 3x = -12
x = -4

If you really have to use substitution,
form the first , 3x = 15y - 12
into the 2nd
15y - 12 + 24y = -12
29y = 0
then 3x = 15(0) - 12
3x = -12
x = -4