Explanation:
2.
x = number of apples
15 (mangoes) = 3x - 6
21 = 3x
x = 7
Mang Jose bought 7 apples.
3.
x = Jack's age
y = Kaye's age
x + y = 27
x = 2y
so, we simply use the identity of the second equation in the first equation :
2y + y = 27
3y = 27
y = 9
x = 2y = 2×9 = 18
Jack is 18 years old.
Kaye is 9 years old.