Consider the diagram below

a$)$ The roller coaster is pulled up to point A where it$,$ and its screaming occupants, are released from rest. Assuming no friction, calculate the speed of the coaster at points B$,$ C$,$ and D$.$ Show your work.

b$)$ Now, suppose the roller coaster passes point A with a speed of $1\mathrm{.}70\frac{m}{s}.$ If the work done by friction is $45,000J,$ with what speed will it reach B$?$ The mass of the coaster is $1000$ kg $.$ Show your work.

I am confused on part b$.$ If you could explain both please that would be amazing.