Answer:
If gravity were stronger, houses and buildings would have to be more sturdy so they do not get crushed to the ground. If gravity were weaker, buildings and houses would have to be built stronger so they do not float away.
Hope this helps you!
Answer:
f = 5 cm
Explanation:
using the thin lens equation, given as follows:

where,
f = focal length = ?
do = the distance of object from lens = 20 cm
di = the distance of image from lens = 6.6667 cm
Therefore,

<u>f = 5 cm</u>