Consider the Supply Curve $Q ^ { s } = 2 P$

Multiple Choice

Consider the supply curve $Q ^ { s } = 2 P$ and the demand curve $Q ^ { d } = 90 - P$ . Which expression best shows how you would calculate the elasticity of demand when $P$ increases by 1 along the demand curve from its equilibrium value?

A) $[ ( 59 - 60 ) / ( 31 - 30 ) ] \times ( 30 / 60 )$
B) $[ ( 56 - 60 ) / ( 31 - 30 ) ] \times ( 30 / 60 )$
C) $[ ( 59 - 61 ) / ( 31 - 30 ) ] \times ( 30 / 60 )$
D) $[ ( 59 - 62 ) / ( 32 - 30 ) ] \times ( 30 / 60 )$