Total Cost in a day is

. Profit function is

. And the revenue function is

. In a day, bookstore must sell at least 15 books, because of 6n-90=0, in order to make profit.
Answer:
(a) The product of the sum of a and b and their difference.

(b) The tripled product of 6a and b².

(c) The difference of the squares of 2m and 7n.

First you plug in the missing values
y=3 x=4 z=2
3÷2×4-2
than you solve
the answer is 4
Given:

He does mistake in the order of giving preference.
We should give preference in the order, division, multiplication, addition, subtraction.
But, he gave the first preferrence to the subtraction.
72-8=64
Next, he used division
64/2=32
Next he adds 32 with 8.
So, he gets 50.
But the actual simplification is,
Simplifying we get,

Hence, the correct value of the expression is 86.
You can gain it by taking an hr and thirty min trip and on the way back takes hr and forty five min. That is how you gain your precious time back!!!✍️☃️⚽️