Question 147089
We basically have this triangle set up:


{{{drawing(500,500,-0.5,2,-0.5,3.2,

line(0,0,0,3),
line(0,3,2,0),
line(2,0,0,0),
locate(-0.2,1.5,10),
locate(1,-0.2,20),
locate(1,2,x)
)}}}

Since we can see that the triangle has legs of 10 and 20 with a hypotenuse of x, we can use Pythagoreans theorem to find the unknown side.



Pythagoreans theorem:


{{{a^2+b^2=c^2}}} where a and b are the legs of the triangle and c is the hypotenuse




{{{10^2+20^2=x^2}}}  Plug in a=10, b=20, and c=x. Now lets solve for x



{{{1 0 0 + 4 0 0 =  x  ^ 2}}} Square each individual term




{{{5 0 0 =  x  ^ 2}}} Combine like terms



{{{s q r t ( 5 0 0 ) = s q r t (  x  ^ 2 )}}} Take the square root of both sides



Which approximates to...


{{{22.3606797749979=x}}}


So our answer is

{{{x=22.3606797749979}}}



which means that 


{{{C=22.3606797749979}}}


It might make more sense to round to the nearest hundredth to get {{{C=22.36}}}



Now take the decimal portion 0.36 and multiply it by 12 to get 0.36*12=4.32


So the length of C is about 22 feet 4.32 inches