Answer:
34feet
Explanation:
Using the pythagoras theorem
Hyp^2 = opp^2 + adj^2
Given
Hypotenuse = 40ft
Opp = 21ft
Required
Adjacent
Substitute
40^2 = 21*2 + adj^2
1600 = 441 + adj^2
adj^2 = 1600 - 441
adj^2 = 1159
adj = √1159
adj = 34.ft
Hence the missing length is 34feet