This is another example of combination system equation with overall 3 unknown values that have been very popular lately. To solve it we need simple math and logic skills. The first line usually consist of 3 same birds. So we need to divide the number at the end of the equation by 3 to find the value of the first bird. The second line include always one of the first birds and another two same birds. So we subtract the value of the first bird from the number at the end of the equation and then divide the result by 2. Now we have the value of the second bird. The third line include one bird from the second line and again two new birds, but in different order. Then again we subtract the the value of the second bird and devide the result by 2. When we have the values of all 3 birds, the last fourth line is to add them to one another by simple addition and find the missing number. This app include the following birds: pigeon, parrot, seagull, flamingo, duck, woodpecker, stork, owl and eagle.