Would someone explain to me where to start.

If x-1 and x+3 are the factors of x3+10x2+ax+b find a and b

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The ages of personnel in the accounting department of a large company are normally distributed with a standard deviation of 7 years. there is a 0.02275 probability that the age of any randomly chosen person in the department is less than 22 and 0.15866 probabilty that the age of any randomly chosen person is greater than 43. what is the mean of this distribution?