Homework Question - Price Floor / Elasticity of Demand
Price elasticity of demand of $-0.5$ means that if price increases by $1\%$ demand decreases by $0.5\%$ (and vice versa in case of decrease).
Consequently, if the equilibrium quantity with floor is $100$ and the price of lettuce is $25\%$ that means that eliminating the price flow - which will offset the $25\%$ will increase the quantity demanded by:
$$0.5\cdot25\% = 12.5\%$$
$12.5\%$ increase from $100$ is $112.5$ so that will be new quantity.
Regarding the price you don't mention what the price at the price floor originally was but it should decrease by $25\%$ from its original value.