Tomatoes from a certain producer have masses which are normally distributed with mean 90 grams and standard deviation 17.7 grams. The tomatoes are sorted into three categories by mass, as follows:

Small: under 80 g;        

Medium: 80 g to 104 g;      

Large: over 104 g.

a. Find, correct to 2 decimal places, the percentage of tomatoes in each of the three categories.

b. Find the value of k such that P(k ø X < 104) = 0.75, where X is the mass of a tomato in grams.