Answer:
day 540
Step-by-step explanation:
He increases his number of situps by 2 each day meaning on day 1 he'd do 2 extra, on day 2 he'd do 4 extra, on day he'd do 6 extra etc. We can show this by saying +2x where x is the day he is on.  Then since he started with 20 we have to add 20 so it would be 20+2x.  We want to know what day it is when he does 1100 situps so we can set our equation equal to 1100 and solve for X which is the day it would be. 
20+2x=1100
2x=1080
I hope this helps and please don't hesitate to ask if there is anything still unclear!
x=540
 
        
             
        
        
        
Gosh, I've done this problem before. Let's start with 13. In this problem, we're basically just skip counting. For example, in the roses row, in the second bouquet, we know we have to add 4 more flowers, so we can document 8. Continue to skip count for both. For 15, we would have about 96 more movie posters remaining, making our ratio 96:x. So, 96:x = 120:100. Therefore, x would equal 80- as 96:80 equals 120:100. If she needs 80 and already had 100, she should sell 20 posters. Hope this helped.
        
             
        
        
        
The answer in 27 $$$$$$$$$$$$$$$$$$$$$$$$
        
                    
             
        
        
        
C. 
You can factor that equation to the following:
x(x - 3)(x + 2) 
Then set each part equal to zero and solve individually.