10 to the power of 3 is 1000, and 400 divided by 1000 is 0.4 because you move the decimal place over 3 in the number 400 to get 0.4.
You could actually find the compositions and thus have something to compare. You haven't shared the list of possible answer choices.
(f+g)(x) = 5x - 3 + x + 4 = 6x + 1
(f-g)(x) = 5x - 3 - x - 4 = 4x - 7
(f*g)(x) = (5x-3)((x+4) = 5x^2 + 20x - 3x - 12 = 5x^2 + 17x - 12
There are also the quotient (f/g)(x) and the compositions f(g(x)) and g(f(x)).
WRite them out.
Then you could arbitrarily select x values, such as 2, 10, etc., subst. them into each composition and determine which output is greatest.
Answer: 
Step-by-step explanation:
We know that the general form of the exponential decay formula is
, where y is final amount remaining after t time, A is the original amount and r is the rate of decay
Now, the ratio of strontium-90 remaining, p , as a function of years, t , since the nuclear accident. 
Hence, the ratio of remaining since the nuclear accident is
Use photomath ! It's an app that gives you the answer with the explanation and it shows you how it got to the answer !
