How many joules do you need to vaporize 1.5 g H2O @ 100 C.
That;s 1.5 g H2O x (2.26 kJ/g) = 3.39 kJ = 3390 J.
What must the final temperature of the Cu be to provide 3390 J energy and end up @ 100 C. That's
3390 = mass Cu x specific heat Cu x (Tfinal-Tinital)
You know mass Cu, specific heat Cu and Tfinal(that's 100 C). Solve for Tinitial
Post your work if you get stuck.