I remember CUP -- concave up positive. Here we have a leading coefficient that's negative, so the cup is upside down, the parabola opens down, an arch not a bowl.
: $55
:
Cost first 3 lines: $11 per line
Cost per additional line: $5
We are interested in 5-line ad, we place 3 lines or less, then we have to pay $11 per line in the ad.
Cost 5-lines = number of lines x cost per line
x = 5 x 11
55
Let V, be the rate in still water and let C = rate river current
If the boat is going :
upstream, its rate is V-C and if going
downstream, its rate is V+C,
But V = 5C, then
Upstream Rate: 5C - C = 4 C
Downstream rate: 5C+C = 6C
Time = distance/Rate, (or time = distance/speed) , then:
Upstream time 12/4C and
Downstream time: 12/.6C
Upstream time +downstream time:= 2h30 ' then:
12/4C + 12/.6C = 2.5 hours
3/C + 2/C = 5/2 (2.5 h = 5/2)
Reduce to same denominator :
5C = 10 and Rate of the current = 2 mi/h
Answer: 
This is 17 to the 1/2 power
The rule is
![\sqrt[n]{x} = x^{1/n}](https://tex.z-dn.net/?f=%5Csqrt%5Bn%5D%7Bx%7D%20%3D%20x%5E%7B1%2Fn%7D)
the n is the index of the root. For square roots, n = 2, so,
![\sqrt[n]{x} = x^{1/n}\\\\\sqrt[2]{17} = 17^{1/2}\\\\\sqrt{17} = 17^{1/2}\\](https://tex.z-dn.net/?f=%5Csqrt%5Bn%5D%7Bx%7D%20%3D%20x%5E%7B1%2Fn%7D%5C%5C%5C%5C%5Csqrt%5B2%5D%7B17%7D%20%3D%2017%5E%7B1%2F2%7D%5C%5C%5C%5C%5Csqrt%7B17%7D%20%3D%2017%5E%7B1%2F2%7D%5C%5C)
