A) $15 ÷ 40% =
15×.4= 6
15+6= 21
B) $38 × .25=9.5
38-9.5=28.50
28.50×.06=1.71
28.50+1.17=30.21
I think this is how you do it. would wait for other answers as well to double check.
At Gino's you pay $16 plus $8 per pizza.
At Venetian's you pay $24 plus $6 per pizza.
Let the number of pizzas be x.
At Gino's you pay 16 + 8x
At Venetian's you pay 24 + 6x
Set the two costs equal and solve for x to find out the number of pizzas for which both costs are the same.
16 + 8x = 24 + 6x
16 + 2x = 24
2x = 8
x = 4
Each place gives you a free pizza.
4 pizzas plus the free pizza equals 5 pizzas.
If you need 5 pizzas (including the free one), both parlors cost the same.
If you need fewer than 5 pizzas, use Gino's.
If you need more than 5 pizzas, use Venetian's.
F(x)=10-16/x
f'(x)=16/x^2
f'(c)=16/c^2
f(8)=10-16/8=10-2=8
f(2)=10-16/2=10-8=2

4∈[2,8] is the required point.
I believe your answer is going to be -6 7/3. Reciprocals are the opposites of a number, so I switched the sign on the 6 and made it -. When dealing with fractions, the reciprocal is essentially just flipping the numerator and denominator, which is how I got 7/3.
I hope I helped. Best of luck!