A right triangle has a base of 6 ft a height off 5ft,what is the length of the opposite side

You have to use the pythagorean theorem to solve this.
a^2 + b^2 = c^2

a = 6ft
b = 5 ft
c = ?

6^2 + 5^2 = c^2
36 + 25 = c^2
61 = c^2
√61 = √c^2

7.810 = c

7.8 feet (rounded to the tenths place)

From pythagraous theorm

6 ^2 + 5 ^2 = x ^2

61 = x ^2
x = root 61

A^2 + B^2 = C^2

So, 36 plus 25 is 61, now find the square root of 61 for your answer, but round to the nearest tenth.

A^2 + b^2= c^2
hypothenuse is c

If you mean the hypotenuse, it is the sqrt of 81.