$Average\ weight_{(Juan,\ Jim,\ Malik)}=\frac{Juan+Jim+Malik}{3}=160\ pounds$

$=>Juan+Jim+Malik=160\ pounds \times3=480\ pounds$

$Average\ weight_{(Juan,\ Jim,\ Malik,\ Harry)}=\frac{Juan+Jim+Malik+Harry}{4}=150\ pounds$

$=>Juan+Jim+Malik+Harry=150\ pounds \times4=600\ pounds$

$=>Harry=600\ pounds-480\ pounds=120 \ pounds$