My tutor was no help

The ratio is 2in to 8mm
so safe to assume 1in represents 4mm.
1in = 4mm

The equation to find the length is:
1.5in = x mm
if we know that 1in is 4mm, 0.5in is 2 mm. So the answer is:
1.5in = 6mm.

The equation to find the width is:
0.75in = x mm
0.75 is 3/4, and 1in = 4mm, so 3/4 of 4 is 3. Therefore,
0.75in = 3 mm

Finally, the answer is:
Length = 6mm
Width = 3mm