Resizing Macro

Hi,

Regularly I have to resize many different designs to as close to 32inchs as possible I usually do this by multiplying the height by the width for example 5.656inches X 5.656inchs =  31.99inches

I have no macro experience but this seems like something that I should be able to make a macro for even though the designs will be different shapes so may be 7.5inches X 4.2585 = 31.938inches etc

What would be the best way for me to go about this?

Any help is very much appreciated!