Question

The sides of the rectangle are given in centimeter 4x+3 on the top 3x+1 on the left x+6y at the bottom 4x-y at the right

Answer 1

so you know that
4x+3 = x+6y
3x+1 = 4x-y

do with that what you will

Answer 2

to be a rectangle, top and bottom must be the same, and left and right
must be the same, so ...
4x + 3 = x+6y ---> 3x - 6y = -3 OR x - 2y = -1
3x+1 = 4x- y ----> y = x-1
using substitution:
x - 2(x-1) = -1
x - 2x + 2 = -1
-x = -3
x = 3 , and y = 2

State your conclusion to whatever question you had, since you did
not ask a question.