Answer:
a.$375
Explanation:
In order to calculate this you just have to keep in mind the amount of months that they paid in advance in the payment, so they had 2 months of rent fully paid in advance, we will represent that with "x", so we have 2x as the number of months, and it doesn´t say that they are paying unequal amounts of money so we will assume that they are paying half each of everything, so the equation will look like this:

If total payment= $1050 each, that means that for the two of them it´d be $2100, now we know that they paid 2 months plus a security deposit of $600, we just have to clear the payment to discover how much does the rent a month cost:

So one month of rent costs $750, if you divide that by 2, you get that Pat´s share of rent a month is $375.