A Fall in the Price of X from $6 to $4

Multiple Choice

A fall in the price of X from $6 to $4 increases the quantity of Y demanded from 900 to 1,100 units.What is the cross elasticity of demand for Y with respect to the price of X?

A) 0.5
B) -0.5
C) 2
D) -2
E) Either 0.5 or -0.5,depending on whether X and Y are substitutes or complements.