Company A : y=0.75x
Company B : y=10+0.50x
x = number of bars purchased
y = cost in dollars
They ask us to calculate the number of bars that must be purchased so that the cost is the same in both companies, that is, that both y(company A) y(company B)
0.75x = 10 + 0.50x
We organize similar terms
0.75x - 0.50x = 10
0.25x = 10
x = 10/0.25
x = 40
40 bars must be purchased so that the cost is the same in both companies.
VERIFICATION
Company A: y=0.75x ---> 0.75(40) = $30
Company B: y=10+0.50x ---> 10 + 0.50(40)= $30
Correct!
The answer to your math question is: Both company A and B must buy 40 bars so that the cost of their purchase is the same in both.