Answer:
a. 30
Explanation:
Equilateral triangle has equal sides and equal angles. Triangles have a total of 180°. 180° divided by 3 (amount of angles) = 60°.
60° = 4/3x + 20 <-- set the equation equal to 60°
40 = 4/3x <-- subtract both sides by 20
x = 30 <-- divide both sides by 4/3, divide 40 by 4/3 by multiplying 40 by the opposite reciprocal, this leaves the variable x isolated and there is your answer