Hello.
First of all, let the number be t.
8 times t can be written like this:
![\mathrm{8t}](https://tex.z-dn.net/?f=%5Cmathrm%7B8t%7D)
Notice that the number is before the variable and the times sign (×) is not there.
We can write it as 8×t, but we usually write it as 8t.
The sum of means we add:
8t+21
Now, "less than" is "<" :
![\mathrm{8t+21 < -16}](https://tex.z-dn.net/?f=%5Cmathrm%7B8t%2B21%20%3C%20-16%7D)
Therefore, the answer is
![\mathrm{8t+21 < -16}](https://tex.z-dn.net/?f=%5Cmathrm%7B8t%2B21%20%3C%20-16%7D)
I hope it helps.
Have a nice day.
![\boxed{imperturbability}](https://tex.z-dn.net/?f=%5Cboxed%7Bimperturbability%7D)