The mass of the piece of lead is calculated using the below formula
Q(heat)= mC delta T
Q = 78.0 j
M=mass =?
C=specific heat capacity ( 0.130 j/g/c
delat T=change in temperature = 9.0 c
by making M the subject of the formula
M = Q/ c delta T
M= 78.0 j/ 0.130 j/g/c x 9.0 c = 66.7 g of lead