we are going to use the heat absorbed formula:
Q = M*C*ΔT
when Q is the heat absorbed = 35.2 J
and M is the mass of iron = 4 g
and C is the specific heat capacity of iron (which we need to calculate)
ΔT the change in temperature = 20-0 = 20 °C
so, by substitution:
35.2 J = 4 g * C * 20°C
∴ the specific heat of this piece of iron C = 35.2 / (4g*20°C)
= 0.44 J/g.°C