let us assume the number of cupcakes sold by Jose = x
Then
The number of cupcakes sold by Janet = 3x
Total number of cupcakes sold by Janet and Jose = 28
Then
x + 3x = 28
4x = 28
x = 28/4
= 7
So
The number of cupcakes sold by Jose = 7
Then
The number of cupcakes sold by Janet = 3x
= 3 * 7
= 21
So the number of cupcakes sold by Janet is 21 and the number of cupcakes sold by Jose is 7.