to produce 4 apples and 4 oranges need $10 (1st condition)
to produce 6 apples and 6 oranges need $15 (2nd condition)
from both condition, we can write it

If we put this information into a system of linier, it'll become x + y = 7.5
it means, fruit stand decide to charge $7.5 for each produce for one apple and one oranges