For the first question, the chance that he/she loses each individual race is $1 - 0.17 = 0.83$. If the races are independent the then probability that she loses them all is $0.83^6$. Subtract that from $1$ for the probability of at least one win.
The second question is too vague for an answer other than "there are formulas for that". Excel knows them and you will learn them when you study statistics.
(For future reference for this site - if you were already a math student I wouldn't have answered this question, since you show no work of your own on it.)
**Edit** in response to comment. Assuming "strike rate" means "probability of winning", $$ 1 - (1 - 0.17)^6 = 0.67 $$ is the probability of winning at least one race out of $6$. For one race out of $100$ the probability is $$ 1 - (1 - 0.17)^{100} = 0.99999999191 $$ so essentially a sure thing. All those decimal places make no real sense.