The rule of scientifinc notation is that we can use number between 0 and 10, so here we can use 2.8. Lets do this
280 000 000 = 2.8 * 100 * 1 000 000
Now we can just multiply 2.8 by 10 to the power of number of 0 reapeted
So [tex]2.8*10^8[/tex] - its the result