Assuming that an exponentiation sign is missing, all you need to know is that rational exponents work like this:
![a^{\frac{b}{c}}=\sqrt[c]{a^b}](https://tex.z-dn.net/?f=a%5E%7B%5Cfrac%7Bb%7D%7Bc%7D%7D%3D%5Csqrt%5Bc%5D%7Ba%5Eb%7D)
So, you have

And similarly,
![81^{\frac{7}{4}}=\sqrt[4]{25^7}=\sqrt[4]{(3^4)^7}=3^7](https://tex.z-dn.net/?f=81%5E%7B%5Cfrac%7B7%7D%7B4%7D%7D%3D%5Csqrt%5B4%5D%7B25%5E7%7D%3D%5Csqrt%5B4%5D%7B%283%5E4%29%5E7%7D%3D3%5E7)
$1.4-0.52=$0.88
So, Joel makes $0.88 profits for every sales.
To overcome rent fee, We need $36.
36/0.88= 40.90909....
So, Joel needs to sell at least 41 iceCream on country fair to make profits.
2/7 = x/10
cross multiply:
10 * 2 = 20
7 * x = 7x
7x = 20
x = 2.857
Circumference formula is πd
C = (3.14)(34)
C = 106.76
Hope this helps :)