The question is.. "The expression 5(3r - 10) means the product of 5 and the difference of three times r minus 10. If r = 4, the value of the expression is [?] This is 6th grade math and im kinda stuck here

Over the course of the school year, you keep track of how much snow falls on a given day and whether it was a snow day. your data indicates that of twenty-one days with less than three inches of snow, five were snow days, while of the eight days with more than three inches of snow, six were snow days. if all you know about a day is that it is snowing, what is the probability that it will be a snow day?