Total mechanical energy: E = (1/2)Mv2 + (1/2)kx2 where M is mass, v is velocity
At 18cm, assuming we start with zero velocity, E = (1/2)*1.1*103*(0.18)^2 Joules
(a) Let xa be the value of x when the PE is 15% of E: (1/2)k*xa2 = 0.15*(1/2)k*(0.18)^2 or xa = sqrt(0.15)*0.18 m
(b) Let va be the velocity at this point. (1/2)*4*va^2 + (1/2)*1.1*103*xa2 = (1/2)*1.1*103*(0.18)^2 solve for va (in m/s)
I'll leave you to do the number crunching.