for the first question you put the right answer, well done!
for the second question:
the missing side is 14.1 ft.
c²= a²+b²
16.7² = x² +8.9²
278.89= x²+79.21
x²=278.89-79.21= 199.68
we want to find x not x² so we square root x² and that gives us the value for x
x=Square root of 199.68
x= 14.1 ft