Ответ:

4A + 8B = 10 ---> 2A + 4B = 10

1) 2B + A = 10 \ 2 = 5

2) 5 \ (A + 2B) = 5 \ 5 = 1

3) A^2 + 4AB + 4B^2 = ( A + 2B)^2 = 5^2 = 25

2A + 4B = 10

вся дробь: 25 \ 10 = 2.5