I'm pretty sure that the answer is 12C4 = (12p4)/4! = (12*11*10*9)/4*3*2*1 = 495
Hope this helps
C
By subtracting 18 to both sides you are separating the 3x because you are not ready to isolate the variable (x) in step 1
The answer to the question
I hope this answer helps, it’s kinda messy, but it’s still understandable (I guess)
Do you just wan't us to answer it or give you an explanation?