Let the number be n
Part A- 2/3 + n = 2n+3
Part B- n= 2/3 -3
n= 2-9 / 3
n= -7/3 =-2.33
The probabilities of knocking down zero, one, and two pins are

and

, respectively. The total probability of knocking down at most two is thus

, or

.
This is the answer -0.25,0.12,6/8