What does below rebus means ?

How many cubic feet of dirt are in a hole of one foot deep, three feet long, and two feet wide?

Can you decipher these quotes by Albert Einstein?
Blf xzm mvevi hloev z kilyovn lm gsv ovevo lm dsrxs rg dzh xivzgvw.

Yesterday I fell from 30 feet high ladder but I don't get hurt. Why?

As a whole I am both
safe and secure.

Behead me and I become
a place of meeting.

Behead me again and I am
the partner of ready.

Restore me, and I become
the domain of beasts.

What am I?

Find the next number in the series below

21 32 54 87 131 ?

John was a very careless driver, so his owner Jacob gave him an offer that he will get an incentive of Rs.30 for every bottle box he delivered without breaking it and he will be charged Rs.90 for every bottle box he broke. Jacob gave John 100 bottles-box to deliver. After delivery, Jacob paid John Rs.2400. How many bottles-box did John break?

If it took eight men ten hours to build a wall, how long would it take four men to build it?

Manish has to secure 40% marks to pass his B.tech final exams.
He got just 40 marks and failed by 40-marks.

What is the maximum marks?

John left on a horse on Thursday , was gone for two days, and came back on Thursday after completing his work. How did that happen?