An Individual Has a Utility Function for Tennis Rackets (X)and $E = \left( \frac { 1 } { 3 } p _ { x } + p _ { y } \right) U$

An individual has a utility function for tennis rackets (x) and tennis balls (y) of the form U(x,y) = min (3x,y) .His or her expenditure function is given by

A) $E = \left( \frac { 1 } { 3 } p _ { x } + p _ { y } \right) U$ .
B) $E = \left( p _ { x } + 3 p _ { y } \right) U$ .
C) $E = \left( p _ { x } + \frac { 1 } { 3 } p _ { y } \right) U$ .
D) $E = \left( p _ { x } + p _ { y } \right) U / 3$ .