Answer:
<HDG = 39°
Explanation:
Red square is a right angle which mean its a 90°
Those two angle <CDG and <HDG are complementary angle which mean they both add up to 90°
<CDG + <HDG = 90°
51° + (3t+15)° = 90°
Solve for t.
3t + 51 + 15 = 90°
3t + 66 = 90°
3t = 24
t = 8
Plug t = 8 into <HDG to find the measurement.
<HDG = 3t + 15
<HDG = 3*8 + 15
<HDG = 24 + 15
<HDG = 39°