Let the number of units of the first type be x and the number of units of the second type be y.
A. You expect to sell at least 100 printers this month. This means that:
A + B >= 100
For simplicity, we will work on the equal sign (A + B = 100) which is the minimum number of units to be sold.
This can be rewritten as: A = 100 - B .................> equation I
B. You expect to make a minimum profit of 4400. This means that:
50A + 40B >= 4400
Again for simplicity, we will work on the equal sign (50A + 40B = 4400) which is the minimum profit to be made
50A + 40B = 4400 ..................> equation II
Substitute with equation I in II:
50 (100-B) + 40B = 4400
5000 - 50B + 40B = 4400
5000 - 4400 = 50B - 40B
600 = 10B
B = 60
Substitute in equation I:
A = 100 - B = 100-60 = 40
Therefore, to minimize your cost and achieve your goals in number of selling units and profits:
you should buy at least 40 units from the first type and 60 units from the second type
I suppose you want to solve the following equation for b:

First of all, you need to divide both sides by 9:

Then, subtract 2 from both sides:

You can say 99 children or 39 children and 44 adults
Ok so 7 times 4 is 28 so she read 28 the first day. For the second day since 40-28= 12, 12 divided by 2 is 6. So she read 6 pages per hour.