Chicken and rabbit have 35 heads and 100 feet. How many do they have? A linear equation with one variable is formulated, Note: it is a linear equation with one variable~

Chicken and rabbit have 35 heads and 100 feet. How many do they have? A linear equation with one variable is formulated, Note: it is a linear equation with one variable~

Suppose there are x chickens and 35-x rabbits, then the equation can be formulated (chicken has two feet and rabbit has four feet)
X*2+(35-X)*4=100
Remove bracket 2x + 140-4x = 100
Shift 2x-4x = 100-140
Merge - 2x = - 40
Coefficient - x = 20
35-20 = 15
A: there are 20 chickens and 15 ducks