Hot water cools from $\;60^{0}\;$ to $\;50^{0}\;$ in the first 10 minutes and to $\;42^{0}\;$ in the next 10 minutes .The temperature of the surroundings is :

Question

$(a)\;25^{0}C \qquad(b)\;10^{0}C \qquad(c)\;15^{0}C \qquad(d)\;20^{0}C$