Plz help with this problem !!

The equation x2 – 1x – 90 = 0 has solutions {a, b}. what is a + b?

Determine the number of girls in a math class with 87 boys if there are 25 girls for every 75 boys

The management of a supermarket wants to adopt a new promotional policy of giving a free gift to every customer who spends more than a certain amount per visit at this supermarket. the expectation of the management is that after this promotional policy is advertised, the expenditures for all customers at this supermarket will be normally distributed with a mean of $95 and a standard deviation of $20. if the management wants to give free gifts to at most 10% of the customers, what should the amount be above which a customer would receive a free gift?