(a) To find the largest possible length of the side of each square he cut out, we need to find the greatest common divisor (GCD) of the lengths of the two sides of the Vanguard sheet. The GCD can be found using the Euclidean algorithm, which states that the GCD of two numbers is the same as the GCD of the smaller number and the remainder of the division of the larger number by the smaller number.
75 cm and 90 cm have a GCD of 15 cm, so the largest possible side length of each square is 15 cm.
(b) To find the total number of squares he cut out, we divide the area of the Vanguard sheet by the area of each square:
Area of Vanguard sheet = 75 cm * 90 cm = 6750 square cm
Area of each square = 15 cm * 15 cm = 225 square cm
Total number of squares = 6750 / 225 = 30
So, Mr. Chua cut out 30 squares of side length 15 cm from the Vanguard sheet