Answer:
x = 6
Explanation:
Complementary angles: 
If sum of two angles add up to 90°, they are called complementary angles.
 75 + 2x +3 = 90
 2x + 78 = 90
Subtract 78 from both sides,
 2x = 90 - 78
 2x = 12
Divide both sides by 2
 x = 12÷2
 x = 6°
2x + 3 = 2*6 + 3
 = 12 + 3
 = 15°