Melting Spheres

Side Note - This is part of the neopets lenny conundrum

There are 3 ice spheres that are differently sized and melting at a rate of 1.5mm/min. The diameters are: .9m , 1.5m , 1.8m. I have their corresponding volumes in cubed meters: .381704 , 1.76715 , 3.05363. The ice is also said to evaporate at .1mm/min.

How do I calculate how much time it will take to completely melt?

This all seems very hard for me, so try to explain something a 9th grader will understand please