What does the below rebus riddle means?

Below, you can see three complete equations and one incomplete. Based on the three complete ones, can you complete the incomplete one?

5 $ 4 $ 3 $ 9 = 4215
6 $ 9 $ 2 $ 6 = 3816
4 $ 7 $ 3 $ 3 = 1122
7 $ 2 $ 7 $ 4 = ____

In case you were starting to feel confident, this one was meant for third graders in Vietnam. The answer is 66, but we don't blame you for scratching your head about how they got there.

In a school, 280 students studied chemistry, 254 students studied physics and 280 students studied biology.

97 students studied chemistry as well as physics, 138 students studied physics as well as biology and 152 students studied chemistry as well as biology.

73 students studied all the three branches.

Can you find out the total number of students?

The day after tomorrow will be three days before Tuesday. Can you find out what is today?

I can be cracked, made, told, and played. What am I?

What does this rebus means ?

PROG WORKRESS

Can you find the company name in the pictogram below?

I have branches, but no fruit, trunk or leaves. What am I?

The LCD device should be able to tell the right time in the format HH:MM: SS in a 12-hour format. You can refer to the picture to get an idea. The device is a simple "level indicator" which has to be converted into a watch. How will you program it to work?