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 consists of 3 same biology cells from teh human body. So we need to divide the number at the end of the equation by 3 to find the value of the first cell. The second line include always one of the first biology cells and another two same biology cells. So we subtract the value of the first cell from the number at the end of the equation and then divide the result by 2. Now we have the value of the second cell. The third line include one cell from the second line and again two new biology cells, but in different order. Then again we subtract the the value of the second cell and devide the result by 2. When we have the values of all 3 biology cells, the last fourth line is to add them to one another by simple addition and find the missing number. This app include the following biology cells: Neuron, Erythrocyte, Leukocyte, Myocyte, Chondrocyte, Gamete, Adipocyte, Osteocyte and Epithelia