Please help will mark brainliest

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

You were told that the amount of time lapsed between consecutive trades on the new york stock exchange followed a normal distribution with a mean of 15 seconds. you were also told that the probability that the time lapsed between two consecutive trades to fall between 16 to 17 seconds was 13%. the probability that the time lapsed between two consecutive trades would fall below 13 seconds was 7%. what is the probability that the time lapsed between two consecutive trades will be between 14 and 15 seconds?

Solve for x and y: 217x + 131y = 913; 131x + 217y = 827