Thank you for the opportunity to help you with your question!

The binomial formula is nCr*Ps^r*Pf^n-r, where n is the number of trials, r is the number of successes, Ps is the probability of success, and Pf is the probability of failure. So plugging in the values we get:

13C7*(.19)^7*(.81)^6

= .00433

Please let me know if you need any clarification. I'm always happy to answer your questions.