How would the pdf asked for in Question 3.3.7 be affected if the particle was twice as

Question:

How would the pdf asked for in Question 3.3.7 be affected if the particle was twice as likely to move to the right as to the left?
In Question 3.37 suppose a particle moves along the x-axis beginning at 0. It moves one integer step to the left or right with equal probability. What is the pdf of its position after four steps?