Cross elasticity of demand [closed]

If Q1=(P2)⅔ 1. Determine the demand for good 1, when the price of good 2 is 8 2. Find the cross elasticity of demand for good 1, with respect to P2, when P2=2

1. $P_2 = 8$, so $Q_1= 8^{2/3}=4$
2. To find the cross price elasticity, differentiate demand for good 1 with respect to $P_2$: $\frac{dQ_1}{dP_2}=\frac{2}{3}P_2^{-1/3}$ When $P_2=2$, cross price elasticity is $\frac{2}{3}(2)^{-1/3}$