Two identical parallel-wired strings of bulbs are connected to each other in series. if the equivalent resistance of the combination is 130 ohms when it is connected across a potential difference of 120 volts, what is the resistance of each individual bulb

You have two things in series (the two strings) and their combined resistance

is 130 ohms. Since they're identical, we can say that the total resistance of

each string is 65 ohms.

With the information in the question, we CAN't tell what the resistance of the

individual bulbs is ... simply because we're not told how many bulbs there are

in the string.

In a parallel circuit, if there are 'N' resistors, and every one has the same

resistance 'R', then the total resistance of the whole parallel combination

is R/N. Example: 10 identical resistors in parallel, the total resistance

of the whole thing is 0.1 of the individual resistance.

So, however many identical bulbs there are in each parallel string ...

call it 'N' ... the resistance of each bulb in the parallel clump is 65N ohms.

"What about the 120 volts?"

Don't need it. Doesn't matter. It has no effect on anything in this discussion.