Even if you don't know anything about electronics and BJTs the riddle can be solved:
You have
* Base current Ib = 100uA (unit: Amperes for current)
* gain= 100 (no unit)
And you want the result to be current => unit = Amperes.
Then there are just two possible mathematical operatiins:
* multiply
* divide
Because you can't add or subtract only values with identical unit.
Ampere - Ampere to get Ampere
or hours - hours to get hours
you can't subtract values with different units: you can't subtract Amperes from hours
But you can multiply and divide values woth different units: like Amperes x hours = Amperehours
Knowing this there are just two possible mathematical results ... whereas only one is in the given results to choose from.