Please answer this correctly

The dimensions are 4 millimetres by 10 millimetres

Step-by-step explanation:

The area of the first rectangle is 5*8=40 square millimetres. Let's call the width of they yellow rectangle w, and the length l. Now you can set up the following system of equations:

l*w=40

2l+2w=28

Isolate one of the variables to substitute:

l=40/w

2(40/w)+2w=28

80/w+2w=28

Multiply both sides by w:

80+2w^2=28w

Move everything to one side:

2w^2-28w+80=0

Factor the quadratic:

2(w^2-14w+40)=0

2(w-10)(w-4)=0

w=4 or 10

l= 10 or 4

Hope this helps!