Answer
temperature of object= 693.67 $^{0}C$
Work Step by Step
Measured frequency of red hot object $ f= 1.0 \times10^{14} Hz$
wavelength corresponding to above frequency $\lambda=\frac{c}{f}$
speed of light $c=3\times10^{8} m/s$
so $\lambda=\frac{3\times10^{8} m/s}{1.0 \times10^{14} Hz}$
$\lambda=3\times10^{-6} m$
$\lambda=3000\times10^{-9} m$
$\lambda=3000 nm$
assuming this wavelength as wavelength corresponding to maximum emission $\lambda_{max}= 3\times10^{-6} m$
From Wiens displacement law
$\lambda_{max} T= 2.90\times10^{-3}m.K$
$T= \frac{ 2.90\times10^{-3}m.K}{\lambda_{max}}$
$T= \frac{ 2.90\times10^{-3}m.K}{ 3\times10^{-6} m}$
$T=0.966666\times10^{3}K$
$T= 966.67 K$
absolute kelvin temperature = temperature in $^{0}C$ + 273
so temperature in $^{0}C$ = absolute kelvin temperature -273
so temperature in $^{0}C$ =966.67 - 273
so temperature in $^{0}C$ =693.67 $^{0}C$