Cm=centimetres
Mm=millimetres
1 meter=100 centimeters
1 meter=1,000 millimeters
So to solve your equation, you divide 140 by 100cm (since he is measured in centimetres)
140cm÷100cm=1.4 meters-is Ben's height
To solve Mike's height, you divide 1090 by 1,000mm (since he is measured in Millimetres)
1,090mm÷1,000mm=1.09 meters-is Mike's height
1.4 meters is greater than 1.09 meters
To see by how much, you subtract 1.4m by 1.09
Mike is taller than Mike by .31 meters or 31 in centimetres or 310 in millimetres