$\left[ g =10 \,ms ^{-2}\right.$ લો.$]$
$t =\sqrt{\frac{2 h }{ g }}=\sqrt{\frac{2 \times 80}{10}}$
$=4 \,sec$
Time taken by ball $B$ to meet $A =2 \,sec$
$\text { using } S=u t+\frac{1}{2} \text { at }^{2}$
$-80=-u \times 2+\frac{1}{2}(-10)(2)^{2}$
$u=30$