The amount of paint required to paint the whole cupboard is:
\(2\times2.5^2+4\times(2.5\times3.5)
\\=47.5 ft^2\)
The amount of paint required to paint all but the bottom surface is:
\(2.5^2 + 4(2.5\times3.5)
\\= 41.25 ft^2\)
So the difference in paint required is 6.25 square feet worth of paint.