How much energy is absorbed when a 50.0 gram magnesium strip is heated from 45 degrees to 90 degrees

Quantity of heat energy required for change of phase= (mass) x (heat of fusion or heat of vaporization), or in equation form Q=mL. Heat of fusion=80cal/g; heat of vaporization=540 cal/g
quanity of heat energy responsible for a temperature change= (mass) x (specific heat) x (change in temperature), or in equation form,  Q=mcT

Here's another way to calculate it  

Calculate the energy absorbed by 20 grams of 100 C water that is turned into 100 C steam
Q=(20g)(540 cal/g)=10,800 cal 

I hope this helps you.

Because a model would make the investigation easier to understand