Answer:
72 inches
Explanation:
We are given that
Length of rectangle=423 inches
Width of rectangle=360 inches
We have to find the side length of the largest square they can use to fill the checkboard pattern completely without overlap or gaps with the help of Euclid's algorithm.
In order to find the largest side of square we will find HCF (432,360).
Euclid's algorithm

a=dividend
b=divisor
q=quotient
r=remainder
a=432,b=360


HCF(432,360)=72
Hence, the side of largest square=72 inches