Notice how the inflow of each node, in this case L + B1 + 0.25 (the 25,000 the task mentions the company already has in month 1) has to be higher or equal to the outflow, which is C2 + a constant equal to the difference between Accounts Receivables and Required Payments which for month 1 would be 30,000 or 0.3 (1.8 - 1.5).
L+B1+0.25 >= C2 + 0.3
rewriting it in standard form then gets you the 0.05 on the RHS:
L+B1-C2 >= 0.05
Edit: the 25,000 also could be seen as C1 which the task mentions is a constant