Gadgets are produced and sold in a competitive market. When there is no tax, the equilibrium price

Question:

Gadgets are produced and sold in a competitive market. When there is no tax, the equilibrium price is $20 per gadget. The own-price elasticity of demand for gadgets is −0.5. If an excise tax of $4 leads to an increase in the price of gadgets to $24, what must be true about the own-price elasticity of supply for gadgets?