I use ratio method.
Total apples of Red:Green is 3:1 which is also 15:5
Total apples sold of Red:Green is 5:1 which is also 15:3
So the green apple remaining is 5-3= 2units
so 2units= 28. 1 unit= 14
Than, 5 units of red apples were sold. so 5 x 14= 70
