differential equation, integral?!

Given that 3x sin2x is a particular integral of the differential equation
d^2 / dx^2 +4y = k cos2x ,
where k is a constant,
(a)calculate the value of k,
(b)find the particular solution of the differential equation for which at
x = 0, y = 2,
and for which at
x= pie/4 y = pie/2