Question

I don’t understand I’m stupid

Answer 1

One mango candy costs 4.20$, so if you buy
`m` mango candies, you'll pay

`4.2m\$`

Similarly, one apple candy costs 4.20$, so if you buy
`a` apple candies, you'll pay

`4.2a\$`

So, the expression to compute the total cost, depending on how many mango/apple candies you buy, is

`T = 4.2m+4.2a=4.2(m+a)`

In your case, since
`a=m=1`, the total cost is

`T = 4.2(1+1) = 4.2\cdot 2 = 8.4`

Answer 2

each candy cost $4.20

T = 4.20m + 4.20a

T = 4.20(1) + 4.20(1) since she bought one mango and one apple

T = 4.20 + 4.20

T = 8.40