Begin with the grammar

S $->$ ASB $|\backslash$epsi

A $->$ aAS $|$ a

B $->$ SbS $|$ A $|$ bb

a$)$ Eliminate $\backslash$epsi productions.

b$)$ Eliminate any unit productions in the resulting grammar.

c$)$ Eliminate any useless symbols in the resulting grammar.

d$)$ Put the resulting grammar into Chomsky Normal Form.