resistivity Ag 15.9e-9 Ω-m
resistivity Fe 100e-9 Ω-m
temperature coefficient of resistivity
α = 0.0038/ºC Ag
R = R₀(1 + α∆T)
4*100 = 15.9(1 + (0.0038)∆T)
400/15.9 = 25 = 1 + (0.0038)∆T
(0.0038)∆T = 24
∆T = 6357ºC
add 25º to get 6382ºC
I believe