The solution for this problem is:
(a). How much the T-shirt cost.
(b). 23=12+x
(c). 23-12=x; x= 11
(d) the T-shirt cost $11.
Answer:
y=2^x
Step-by-step explanation:

This result is actually true for any exterior angle. The exterior angle of a triangle is equal to the sum of the two remote angles, and above is a short proof of it.