Christian, this is the solution:
C1 = 0.19t
C2 = 34.95 + 0.09t
We need to calculate C1 = C2, therefore:
0.19t = 34.95 + 0.09t
Like terms:
0.19t - 0.09t = 34.95
0.1t = 34.95
Multiplying by 10 at both sides:
0.1t * 10 = 34.95 * 10
t = 349.5
The plans will have the same cost, if you talk for 349.5 minutes