John and Mark have each committed to charity each week for the next year. Their weekly incomes are independent of each other. Suppose the amount donated in a week by John is normally distributed with a mean of $37 and a standard deviation of $8, and the amount donated by Mark is also normally distributed with a mean of $45 and a standard deviation of $4. Estimate the number of weeks in a 52-week year that their combined donation will exceed $93?