Here is some data about a group of boys and a group of girls. Boys: number: 20
mean height: 1.55 m
range of heights: 0.42 m

Girls: number: 10
mean height: 1.40 m
range of heights: 0.36 m

For the combined group of boys and girls, work out, if possible:
a the number of children
b the mean height
c the range of heights.​