He bought three $10 shirts and six $7 shirts.
143 is composite. To be prime it has to have only 2 divisors i.e it's self and one but since it has 4 divisors ( 143, 1, 11 and 13) it is composite.
6+8+5=19
Probability= 8/19=0.42= 42% of picking green.
(1-z) can combine with other coupons
