Algebra Word Problems! HELP!?

Question

I got this stupid worksheet and i don't understand how to do these two problems... I need help today!

3. There are 40 cows and chicken in the farmyard. One quiet afternoon, Lack counted and found that there were 100 legs in all. How many cows and how many chickens are there?

a. Solve this problem by writing and solving an equation.

4. Assume that a, b, and c are integers and a≠0. Prove that the solution of the linear equation ax-b=c must be a rational number.

Answer 1

3.        let x= # of cows y= # of chickens

        4x + 2y= 100  sry thats about all i can rite now....

Answer 2

3. Cows have 4 legs. Chickens have 2 legs.

Let x= number of cows

Let y= number of chickens

x+y= 40 ---Number of animals

4x+2y= 100 ---Number of legs

x+y= 40

x= -y+40 ---Subtract y from both sides.

4x+2y= 100

4(-y+40)+2y= 100 ---Substitute (-y+40) for x.

-4y+160+2y= 100 ---Distribute 4 to (-y+40).

-2y+160= 100 ---Simplify.

-2y= -60 ---Subtract 160 from both sides.

y= 30 ---Divide both sides by -2.

x+y= 40

x+30= 40 ---Substitute 30 for y.

x= 10 ---Subtract 30 from both sides.

There are 10 cows and 40 chickens.

4. ax-b= c

ax= b+c ---Add b to both sides.

x= (b+c)/a ---Divide both sides by a.

a, b, c are all integers, with a≠0. Therefore the solution, x, cannot be undefined and must be a rational number.