Math Brain Teasers.?

Question

Once again i am at a lost.

if f(x), defined for all real x, satisfies f(1-x) + 2f(x), express f(x) as a polynomial in x.

and the other one is :

In 1988, the population of A increased by 20% while the population of C decreased by 10%, after which the two populations were equal. What percent of the original population of cadabra was the original population of A?

i think the answer is 30% but please check. i need the first one the most.

thank you

Answer 1

1.2A = 0.9C

A = 0.9C/1.2

A = 0.75C

original population of A was 75% of original population of C