for this case we have:
x: variable that represents the number of minutes jackie runs.
y: variable that represents the number of minutes jackie dances.
according to the data we have:
x + y = 55\\25 + x = y
to solve the system, we substitute the second equation in the first one:
x + 25 + x = 55\\2x = 55-25\\2x = 30\\x = \frac {30} {2}\\x = 15
so, jackie runs 15 minutes a day.
y = 25 + x\\y = 25 + 15\\y = 40
so, jackie dances 40 minutes a day.
it is not possible that jackie has spent 45 minutes dancing in one day. since he dedicates 55 minutes to both activities, he runs 15 minutes and the rest dances.
part a:
x + y = 55\\25 + x = y
part b:
jackie runs 15 minutes per day.
part c:
it's not possible.