Final answer:
The question seeks an expression for the balance in a joint account after m months given initial and subsequent deposits by two individuals. The best fitting answer without additional information on the monthly deposit amount is 240m, representing the collective monthly deposit assuming they each contribute $120 monthly.
Step-by-step explanation:
The question asks about the expression representing the account balance after m months when two people, Sophia and Ollie, collectively make monthly deposits into a joint bank account.
They each deposit $120 initially to open the account and presumably continue with the deposits monthly, though the question does not specify the amount of subsequent deposits.
Assuming that the initial deposit of $120 each is the only deposit Sophia and Ollie make, the total initial deposit would be $120 + $120 = $240. If they continue to deposit this amount every month, then after m months, they would have deposited 240m.
However, the question's details are not explicit about the amount deposited monthly after the initial deposit. If Sophia and Ollie deposit a different amount per month, the expression could vary. Without additional information, the most fitting answer from the given choices would be 240m, where 'm' represents the number of months.
Therefore,the correct answar is b) 240m