c4 differentiation QSN, some1 help plizz

At time t=0, a tank of height 2metres is completely filled with water. water then leaks from a whole in the side of the tank such that the depth of water in the tank, 'y' metres, after 't' hours satisfies the differential equation :

dy/dt = -k

Unparseable latex formula:

e^

^(-0.2t)
where k is a positive constant

a) find an expression for 'y' in terms of k and t
given that 2 hours after being filled the depth of water in the tank is 1.6 metres,
b) find the velue for k to 4 sig.figures

c) given also that the whole in the tank is 'h' centimetres above the base of the tank, show that 'h' = 79 to 2 sig.figures




for part a, i intergrated that dy/dt , then substituted the y and t values to work out k(for part b)
i think i did somethin wrong in the process thoh

in part C, im trying dy/dx =0, im not sure bout this thoh

could some1 show me how to do this qsn pliz

thanks, i wasnt adding the 'C' for some reason