Mass = 100g = 0.1kg

Specific heat = 4.8 J/(kg x c)

del T = (100-30) degree celcius = 70 degrees celcius

Heat Loss = mass x specific heat x del T

= (0.1 x 4.8 x 70) J

=  33.6 J

So, the loss of heat when 100 g of iron is cooled down from Temperature of 100 degrees celcius to a Temperature of 30 degrees celcius is 33.6 J.