You first multiply the 8 in 308 to the 9 in 1809, then the 0, then the 9, then finally the 1 in 1809. For the tens place, don't forget to put a zero under the ones place because that's not where you start. So for 0 everything is 0 so just put a line of 5 zeros in the second row. Lastly, the 3 multiplies to 9, 0, 8, and the 1 in 1809. In the 3rd row, put 2 zeros because you're multiplying to get the hundreds place. Line and add them all up to get 557152. Hope this helps!
With composition of functions (as with the order of operations) we perform what is inside of the parentheses first. So, g(3)=2(3)+2=8 and then f(8)=24.