18. s = 5r^2 + 7......making r the subject
      s - 7 = 5r^2
      (s - 7) / 5 = r^2...by taking the sqrt of both sides, it eliminates the ^2
     ( sqrt (s-7)/5) = r
19. h = ut - 1/2gt^2....u = 100, t = 1 4/5(or 9/5)...g = 6.4
      h = (100)(9/5) - 1/2(6.4)(9/5^2)
      h = 180 - 1/2(6.4)(3.24)
      h = 180 - 3.2(3.24)
      h = 180 - 10.368
      h = 169.632 or 169 79/125
20. sorry..do not know this one
        
                    
             
        
        
        
Answer:
Option C i.e. 2 and 9, constants have a fixed value is a correct option.
Step-by-step explanation:
In algebra, a constant is basically a fixed value.
Sometimes, a constant is a number for a letter such as a, b, or c for a fixed number.
For example: in ''2x+7=3'', 7 and 3 are constants.
- <em>Please note that the number with variable x in the term is a coefficient.</em>
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In our case:
Given the equation

Therefore, 2 and 9 are constants, having a fixed value.
Thus, option C i.e. 2 and 9, constants have a fixed value is a correct option.
 
        
             
        
        
        
(40 min)/(5 mi) = (time)/(7 mi) . . . . . the rates are the same
(7/5)*(40 min) = time = 56 min
At the same rate, it would take Petra 56 minutes to jog 7 miles.
        
                    
             
        
        
        
Answer:
16.5 hours
Step-by-step explanation:
The bicycle costs $240.  Eva already has $42.  She is making $12 per hour.
240 = 12x + 42
Solve for x to find out how many hours Eva needs to work to buy the bicycle.
240 = 12x + 42
240 - 42 = (12x + 42) - 42
198 = 12x
198/12 = (12x)/12
16.5 = x
Eva needs to work 16.5 hours to be able to buy the bikw.