Find the scale factor of a construction plan if the scale is 0.75 centimeters = 3 meters.

Typically a plan is much smaller in size than is the object or structure to be built.  Converting 0.75 cm into meters and then dividing the result into 3 meters will give you a positive scale factor greater than 1.

Note that we can convert 0.75 cm into m by multiplying 0.75 cm by the conversion factor

1 meter

100 cm

Please do this now.  
Next, divide your result into 3 meters to obtain the scale factor.