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

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

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

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

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