Actually the variables are already stated.

B=bank

w=week

B<=750-20w

The reason why it's <=:

In the problem, she draws$20 per week. She could take outat leastthan $20.more

Therefore, at a certain time, if she takes out, what she has in the bank will be, B<750-20w. (750 is the principal amount she has)more than $20

If she only takes out $20 each time, she'll have, B=750-20w, in the bank.

Hence the inequality, B<=750-20w.