Let
D=no. of dance minutes
R=no. of run minutes
(A)
She runs and dances for a total of 55 minutes =>
D+R=55
She dances 25 minutes more than she runs =>
D-R=25
(B)
This is called a sum and difference problem where the larger value (D) is obtained by D=(55+25)/2=40
and the smaller value R=(55-25)/2=15
Check: 40+15=55, 40-15=25 ok
(C)
It is possible she spends any time dancing, but it won't satisfy the given conditions unless D=40