Three grades of a normal distribution of egg masses shown on a normal curve, and the two grade boundaries by inverse normal

The masses of eggs from a poultry farm are normally distributed. Each egg is graded as small, medium or large. The lightest \(18.41\%\) of the eggs are graded small and the heaviest \(6.68\%\) are graded large. The remaining eggs, with masses between \(r\) grams and \(t\) grams, are graded medium.

1. On the diagram below, mark the positions of \(r\) and \(t\) and write the percentage of eggs in each grade.[2]
2. The mean mass of the eggs is \(58.5\) grams and the standard deviation is \(4.2\) grams. Find the value of \(r\) and the value of \(t\).[5]