I WILL GIVE YOU 20 POINTS TO THOSE WHO ANSWER THIS QUESTION RIGHT NOOOO SCAMS AND EXPLAIN WHY THAT IS THE ANSWER

Answer:
78°
Step-by-step explanation:
the whole measure of a triangle =180° =3angles plus together
the 1st + 2nd angle = 90°+12°=102°
the 3rd angle = 180°-102°=78°