They are basically like groups. Take -3x+2x , Just do -3 +2 = -1 and then just add the x. So -1x. Next you have -5y+10y . Just do -5 + 10 = 5 and remember to add the x on so your final answer should be -1x + 5y
The slope within two sets of points is calculated using the slope equation 
<h3>What is slope?</h3>
The slope of a line or points is the rate of change of the line.
This in other words means that, the vertical change per unit horizontal change
Assume that the points are given as:
(x1, y1) and (x2, y2)
The slope (m) of the points is:

Hence, the equation of two sets of points is 
Read more about slopes at:
brainly.com/question/1884491
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Your formula here is A=pir^2
Plug in the numbers but instead use 22/7 for pi
A=(22/7)(21)^2
A=22/7*441=1386
Answer is 1386 sq inches