Let
x -----> the number of cows
y -----> the number of chickens
we know taht
x+y=100 ------> equation A
4x+2y=286 ------> equation B
solve the system of equations by graphing
remember that the solution is the intersection point both graphs
using a graphing tool
see the attached figure
the solution is (43,57)
therefore
43 cows
57 chickens
we have the system
x+y=100 --------> equation A
4x+2y=286 -------> equation B
step 1
isolate the variable x in equation A
x=100-y -------> equation C
step 2
substitute equation C in equation B
4(100-y)+2y=286
solve for y
400-4y+2y=286
-2y=286-400
-2y=-114
y=57 chickens
Find the value of x
substitute the value of y in equation C
x=100-57
x=43 cows
This method is called solve the system by substitution