When solving practical problems with equations, the quantities on both sides of the equation must be ()

When solving practical problems with equations, the quantities on both sides of the equation must be ()

When solving practical problems with equations, the quantities expressed on both sides of the equation must be equal
Do not understand can ask, help please adopt, thank you!

Write an application question, must have 2 and 2.5 two data. List the corresponding equation to answer

There are 100 parts. If master Zhang makes them by himself, it takes 2.5 hours. How to work with his apprentice takes 2 hours. How long does it take for him to make them by himself?
Set up apprentices to produce X parts per hour
2(100/2.5+x)=100
The solution is x = 10
100 / 10 = 10 (hours)

There are 12 chicken and rabbit legs, six more than chicken legs, how many chicken and rabbit each?
There are 12 chickens and rabbits in total. There are six more rabbit legs than chicken legs. How many chickens and rabbits each?
How to get a few rabbits and chickens?
First grade math problem. Dizzy
Please answer before the 9th

It's a grade one math problem. It's easy to understand
A rabbit has four legs and a chicken has two
Suppose there are six chickens and six rabbits, then the chicken's leg is 12 and the rabbit's leg is 24
If you turn a rabbit into a chicken, the chicken's legs are 14, and the rabbit's legs are 20
So their feet are just six
So there are seven chickens and five rabbits