Problem 3.32

DSolve[{P'[t] == -2 P[t] + 25, P[0] == 1}, P[t], 
      t]

DSolve[{P'[t] == -2 P[t] + 1, P[0] == 1}, P[t], 
      t]

DSolve[{P'[t] == -2 P[t] + 5, P[0] == 0}, P[t], 
      t]