What does below chemistry rebus means?

What does this simple rebus mean?

81 x 9 = 801. What must you do to make the this equation true?

The cream is heavier than Milk. True or False?

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

How will you measure 15 minutes using two hourglasses of 7 minutes and 11 minutes respectively?

What jumps when it walks and sits when it stands?

What does this rebus riddle means ?

A large water tank has two inlet pipes (a large one and a small one) and one outlet pipe. It takes 3 hours to fill the tank with the large inlet pipe. On the other hand, it takes 6 hours to fill the tank with the small inlet pipe. The outlet pipe allows the full tank to be emptied in 9 hours.

What fraction of the tank (initially empty) will be filled in 0.64 hours if all three pipes are in operation? Give your answer to two decimal places (e.g., 0.25, 0.5, or 0.75).

What does below Rebus say?

XLR8