The Value of an Economic Variable Over Time Satisfies the Relation

Multiple Choice

The value of an economic variable over time satisfies the relation
$R ( t ) = \frac { 6 } { 1 + t ^ { 2 } } + 3 e ^ { - 0.4 t }$ , Find the equilibrium value of $R$ .

A) it does not exist
B) 3
C) 0
D) 9
E) 6