Hello.
First of all, let the number be t.
8 times t can be written like this:

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 "<" :

Therefore, the answer is

I hope it helps.
Have a nice day.

Answer:
x=10/-3, 4/5
Step-by-step explanation:
f(x) = (10 - 3x)(4 - 5x)
10-3x=0
-3x=-10
x=10/3
4 - 5x = 0
-5x = -4
x = 4/5
Subtract the 12x^2 first.
5x - 4 = 6
Add the four
5x = 10
Then divide the 5 from both sides
X = 2