Answer:
8.3
Explanation:
The Pythagorean theorem helps you find AD:
AD² +CD² = AC²
AD = √(AC² -CD²) = √(5² -4²) = √9 = 3
The triangles in the figure are all similar, so
BD/CD = CD/AD
BD = CD²/AD = 4²/3 = 5.333
Then
AB = AD +BD = 3 + 5.333
AB = 8.333 . . . . rounds to 8.3