Robert is a boy, so you only need the formula for a boy’s predicted height.
father’s height=x
fathers height=180
so, x=180
mother’s height=y
mother’s height=160
so, y=160
plug in x=180 and y=160 into the formula.
0.4(x+y)+42
0.4(180+160)+42
use GEMDAS to simplify.
G(Groupings)
0.4(180+160)+42
0.4(340)+42
M(Multiplication)
0.4(340)+42
136+42
A(Addition)
136+42
178
The predicted height of Robert when he is an adult is 178 cm.