135. To get from one number to the next, you have to divide by 3. Since multiplication is the opposite of division, you have to multiply the second number in the sequence, 45, by 3 in order to get the first number, which is 135.
The events 'select a plain pencil' and 'select a color pencil' are independent. therefore the probability of both occurring is the product of their probabilities: The answer is 3/20 or 0.15.
