Who could help me on the last part

The pyramid below was dissected by a horizontal plane which shape describes the pyramid horizontal cross section

In the field of thermodynamics, rankine is the unit used to measure temperature. one can convert temperature from celsius into rankine using the formula , what is the temperature in celsius corresponding to r degrees rankine? a. 9/5(c - 273) b. 9/5(c + 273) c. 5/9( c - 273) d. 5/9( c + 273)

Consider the sequence below. 3 , 1 , 1/3 , 1/9 , select the explicit function which defines the sequence.