A) since total height of 4 boys is given as 700cm,
Average height of boys = 700cm/4 = 175cm

B) given the”new “ average height now after boys are added = 163cm

Difference in the average height of boy now is
= 175cm -163cm = 12cm decrease

Difference in an avg ht of a girl now
= 163cm -157cm =6cm

12 / 6= 2

Since the average height of boys is “decreased” this tells us there has to be more girls than boys. Therefore number of girls = 4x 2 = 8

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To check:
Total number of children now = 4+ 8 = 12
Where total height of girls now
= 8x 157cm =1256cm

Total height of children
= 700cm (4boys) + 1256cm
=1956cm

Average ht of children = 1956/12 = 163cm (therefore answer is correct, with 8 girls)