Lexi answers 45 questions correctly on a test and earns a 90%. How many questions were on the test?

Math it's appreciated. (picture provided)

An office supply company conducted a survey before marketing a new paper shredder designed for home use. in the survey, 80 % of the people who tried the shredder were satisfied with it. because of this high satisfaction rate, the company decided to market the new shredder. assume that 80 % of all people are satisfied with this shredder. during a certain month, 100 customers bought this shredder. find the probability that of these 100 customers, the number who are satisfied is 69 or fewer.

Find an bif a = {3, 6, 9, 12) and b = {2, 4, 6, 8, 10).