Answer
The area remaining in the triangle is $A=593~cm^{2}$
Work Step by Step
The remaining area of the triangle (let's call it $A$) is the total area of the equilateral triangle minus the area of the square hole.
The formula to calculate the area of an equilateral triangle is $A=\frac{\sqrt 3a^{2}}{4}$.
The formula to calculate the area of the square hole is $A=s^{2}$.
Subtracting these two areas gives:
$A=\frac{\sqrt 3a^{2}}{4}-s^{2}=\frac{\sqrt 3(40cm)^{2}}{4}-(10cm)^{2}=592.83cm^{2}\approx 593~cm^2$
