If you are a freshman, you haven't learned binary linear equations, have you?

You can do it.

Let the length be a and the width be (60-a)/4.

Then a+2x (60-a)/4 = 21+3x (60-a)/4.

a+( 120-2a)/4 = 2 1+( 180-3a)/4

4a+ 120-2a = 84+ 180-3a

5a= 144

a=28.8

The width of the small rectangle is: (60-28.8)/4=3 1.2/4=7.8.

The width of the large rectangle is: 2 1+3X7.8=44.4.

So the shaded part is

66X44.4-28.8X7.8=2705.76

I can't guarantee that the calculation is completely correct.

But here's the method. exactly

You said first grade.

So it can be calculated like this.

I am a junior high school teacher.

I haven't learned binary linear equation in grade one.

I hope this idea can give you some help.