answer to the first part is also similar to that of the second part i.e.-

 

u=4.50x10^5m/s

s=0.375m

a=F/m

=> a=Eq/m

 

put E= -1.50V/m(since direction is opposite)

q= -1.6x10^ -19C

m=9x10^9kg

 

then use the equation of motion -

 

v²=u²+2as