Answer:
48 h
Step-by-step explanation:
Think of it this way.
Jacob can complete 1/24 of the app per hour. His friend can complete 1/x of the app. Together they complete the app in 16 h.
Jacob's portion + friend's portion = 1
16/24 + 16/x = 1
2/3 + 16/x = 1 Multiply each side by 3
2 + 48/x = 3 Multiply each side by x
2x + 48 = 3x Subtract 2x from each side
x = 48
It would take his friend 48 h to complete the app alone.
Check:
16/24 + 16/48 = 1
⅔ + ⅓ = 1
1 = 1
Thus, in 16 h, Jacob completes two-thirds of the app and his friend completes one-third.
