Problem $2(30$ points$)$

A two stage rocket has the following stages:

Stage $1$: mass propellant $2100000$ kg $,$ mass structure $135000$kg$,$ specific impulse is $263$ s

Stage $2$: mass propellant $450000$ kg $,$ mass structure $35000$ kg $,$ specific impulse is $421$ s

The mass of the payload is $150000$ kg

Find the velocity of the rocket at the end of the propellant burn of the second stage. Assume uncorrected specific impulses, zero initial velocity.