We know that,
cooling rate is directly proportional to difference of temperature of body and temperature of surroundings
$$\dfrac { d\theta }{ dt } \propto ({ \theta }_{ t }-{ \theta }_{ s })\\ $$
$$\dfrac { d\theta }{ dt } =k({ \theta }_{ t }-{ \theta }_{ s })$$ --------------------------(1)
Given,
$$ At\quad { 75 }^{ \circ }C\quad ,\dfrac { d\theta }{ dt } ={ 4 }^{ \circ }C/min$$
And
$$ At\quad { 55 }^{ \circ }C\quad ,\dfrac { d\theta }{ dt } ={ 2 }^{ \circ }C/min$$
Substitute all value in equation(1)
$$4=k(75-{ \theta }_{ s })$$ ---------------------------------------(2)
And
$$2=k(55-{ \theta }_{ s })$$ ----------------------------------------(3)
By Dividing both the above equation we will get
$$\dfrac { 4 }{ 2 } =\dfrac { k(75-{ \theta }_{ s }) }{ k(55-{ \theta }_{ s }) }$$
$$\ { 2 } =\dfrac { (75-{ \theta }_{ s }) }{ (55-{ \theta }_{ s }) }$$
$$2(55-{ \theta }_{ s })=(75-{ \theta }_{ s })$$
$$110-{ 2\theta }_{ s }=75-{ \theta }_{ s }$$
$$110-75=2{ \theta }_{ s }-{ \theta }_{ s }$$
$${ \theta }_{ s }=35$$
Hence, Temperature of surroundings is 35 degree celcious.Hence, Option (D) is correct option.