Hey there mate :)
As per question, AB + BC = AC are the sides of a triangle.
=> AB + BC = AC
( AC is hypotenuse and AB and BC are remaining two sides )
=> (x + 16) + (4x + 11) = 77
(These are the given values of each side such as [x+16]=AB ; BC=[4x+11] and AC=77)
=> 5x = 77 - 27
=> 5x = 50
=> x = 50/5
=> x = 10
( Now these above steps are the continuing solving processes of given values)
=> AB = x + 16
(Previously we got value x and now substitute its value)
=> AB = 10 + 16
=> AB = 26
(Now these are the remaining solving processes)
~ Benjemin360