Answer:
15
Step-by-step explanation:
Since the total degrees of ANY triangle is 180 degrees, start by subtracting 63 and 45 by 180.
180-63-45=72
Now take the 12 from (4x-12) and subtract that from 72.
72-12=60
Now divide 60 by 4 from the 4x.
60/4=15.
