(1) let "r" denote number of rabbits, "c" number of chickens
Set up the equations:

Answer: There are 575 rabbits and 425 chickens
(2) m - number of Mike's stamps, a - number of Andrew's stamps.
Set up equations:

Answer: Mike has 48 stamps. Andrew has 12 stamps.
Answer:
-1280
Step-by-step explanation:
There are 2 ways you could do this. You could just do the question until you come to the end of f(4). That is likely the simplest way to do it.
f(1) = 160
f(2) = - 2 * f(1)
f(2) = -2*160
f(2) = -320
f(3) = -2 * f(2)
f(3) = -2 * - 320
f(3) = 640
f(4) = - 2 * f(3)
f(4) = - 2 * 640
f(4) = - 1280
I don't know that you could do this explicitly with any real confidence.
A+30 = 60
a = 30
a + 2b = 60
30+2b = 60
2b = 30
b = 15
5b - 5c = 60
5(15) - 5c = 60
5c = 15
c = 3
10c + d = 60
10(3) + d = 60
30 + d = 60
d = 30
2d + 6e = 180 - 60
2(30) + 6e = 120
6e = 60
e = 10
4f + 4e = 120
4f + 4(10) = 120
4f = 80
f = 20