Heat absorbed to raise the temperature is given by
[tex]Q = mc\Delta T[/tex]
here
m = mass
c = 7.11 J/g C
[tex]\Delta T = 303 - 298 = 5 kelvin[/tex]
Q = 138 KJ
Now by using the above formula we will have
[tex]138 * 10^3 = m* 7.11 * 5[/tex]
[tex]m = 3881 gram[/tex]
[tex]m = 3.88 kg[/tex]
So the amount of the substance will be 3.88 kg