Correct Answer - B
(b) Given mass, m=5 kg
Acting force,`F=(-3 hati+4 hatj)ms^(-1)`
Initial velocity at t=0,u=`(6 hati+12 hatj)ms^(-1)`
Retardation, `capa=(F)/(m)=(-(3hati)/(5)+(4hatj)/(5))ms^(-2)`
As final velocity is along Y-axis only, its x-component must be zero.
From v=u+at, for X-component only, `0=6hati-(3hati)/(5)t`
`t=(5xx6)/(3)=10s`