Jon makes a mix of salad that cost $15 using as much apples that cost $4/kg as oranges that cost $6/kg. how much of each fruit is in the salad?

Let
 x = number of apples.
 y = number of oranges.
 we have to write the following equation to represent the problem:
 4x + 6y = 15
 To satisfy the equation, Jon must have used
 x = 2.25
 y = 1
 Substituting
 4 (2.25) +6 (1) = 15
 9 + 6 = 15
 answer
 Jhon used 2.25kg of apple and 1kg of orange to make the salad.
 Note: Since the problem does not have any other restrictions, there may be several apple and orange combinations that cost $ 15 per salad.