Following a breakthrough in photovoltaic manufacturing, the average retail price of residential solar panels decreases by 15%. If the cross-price elasticity of demand (XED) between solar panels and residential storage batteries is -1.2, what is the expected percentage change in the quantity of storage batteries demanded?
−18%-18\%−18%
+18%+18\%+18%
−12.5%-12.5\%−12.5%
+12.5%+12.5\%+12.5%