Answer
$t=11s$
Work Step by Step
We know that
$tan\theta=\frac{h}{d}$
or $d=\frac{h}{tan\theta}$
put the values
$d=\frac{5000}{tan42^{\circ}}=5553m$
Now we can find $t$
$t=\frac{d}{v_s}$
given that speed of plane i.e $v_s=1.5 Mach$
we know that
$1 Mach=331 \frac{m}{s}$ (that is speed of sound)
$1.5 Mach=1.5\times331=496.5\frac{m}{s}$
so $v_s=496.5\frac{m}{s}$
putting the values, we get
$t=\frac{5553}{496.5}=11.18s=11s$
$t=11s$
