A textbook store sold a combined total of 386 chemistry and physics textbooks in a week. The number of chemistry textbooks sold was 84 more than the number of physics textbooks sold. How many textbooks of each type were sold?

240

Step-by-step explanation:

We have two types of textbooks. Let's use "x" to represent the number of math textbooks and "y" to represent the number of history textbooks.

Altogether, the bookseller sold 240 math and history textbooks. So:

x + y = 240

Now, the number of history textbooks sold was 72 less than the number of math books sold. So:

y = x - 72

Now we can substitute for y in the equation and solve:

x + y = 240

x + (x - 72) = 240

2x - 72 = 240

2x = 312

x = 156

The bookseller sold 156 math textbooks.

Since y = x - 72, he must have sold 84 history textbooks.

Let's check our answers:

x + y = 240

156 + 84 = 240

That is true, so we did get the correct answers.

Y= 4/5 x + 24
To find the rate of change you find the difference in each of the numbers on the graph. For example, 36-32 is 4. So 28-4 is 24 and that would be the next number down. It would also match x to be 0 because since the rate of change for x was 5, if you subtract 5 from 5 you get 0. So from this we know that the coordinates would be 0,5.
From this info, the slope would be 4/5 and the y intercept or initial value would be 24