Monetary policy when the economy is in a liquidity trap

Suppose that money demand is given by:
M& = $Y(0.25 − i)
if interest rates are positive. This question refers to the situation where the interest rate is zero.
a. What is the demand for money when interest rates are zero and $Y=80?
b. If $Y=80, what is the smallest value of the money supply at which the interest rate is
zero?
c. Once the interest rate is zero, can the central bank continue to increase the money supply?
Why or why not?
d. Graphically show the effect of monetary policy on money markets when interest rates are
zero (at the zero lower bound). Explain your answer (the shape of the money demand
curve, and the effect of monetary policy).