Answer:
The correct answer is not shown in your picture. You must get a = 60.
Explanation:
(1/2)a + (2/3)b = 50
b = 30
(1/2)a + (2/3)(30) = 50
(1/2)a + 20 = 50
(1/2)a + 20 - 20 = 50 - 20
(1/2)a = 30
2 * (1/2)a = 2 * 30
a = 60
The correct answer is not shown in your picture. You must get a = 60.