Correct Answer - B
The area of each rectangular sheet cut out `=3xx5=15cm^(2)` and the area of the square piece of aluminium sheet = `10^(2)=100cm^(2)`
The total area of the rectangular sheets cut out = `4xx15=60cm^(2)`
The area of the aluminium sheet leftover = Area of square sheet - Total area of the rectangular sheets cut out
`therefore` The area of the aluminium sheet leftover = `100-60=40cm^(2)`