Question 1137244
.
<pre>
Mathematical model is this equation


    (30-2x)*(80-2x) = 1776,


where x is the length of the square under the question.


Simplify and solve, step by step


    2400 - 160x - 60x + 4x^2 = 1776

    4x^2 - 220x + 2400 - 1776 = 0

    4x^2 - 220x + 624 = 0

    x^2 - 55x + 156 = 0

    {{{x[1,2]}}} = {{{(55 +- sqrt(55^2 - 4*156))/2}}} = {{{(55 +- 49)/2}}}.


The two roots are  52  and  3.

Of them, only x= 3 is meaningful.


(The other root x= 52 makes the dimensions of the new base negative !).


<U>ANSWER</U>.  the side of the square is 3 cm.


<U>CHECK</U>.   (30-2*3)*(80-2*3) = 24*74 = 1776 square centimeters.   ! Correct !
</pre>

Solved.