I may be misundstanding your question, but this looks like a simple input/output function of the for y = mx + b. If we make a table of values, then we have x values of 8, 3, unknown, unknown, 7. Cooresponding y values are unknown, 21, unknown, 28, 49. If we assume this is the case, then we can determine the slope between the two points of (7,49) and (3,21) by using the slope formula: the difference in y values divided by the difference in x values. So 49-21 over 7-3 which yields 28/4 or 7. Therefore, the slope for this set of values is 7. Plug this value of slope (or m) into y = mx + b, and we have y = 7x + b. If we substitue either point we used above into this equation we find 49 = 7(7) + 0 and 21 = 7(3) + 0. We use zero for b, since the equation is true only if b = 0. So the first output blank is y = 7(8) or 56. The last input blank is 28 = 7(x), so solving for x we find x = 4. The middle unknown input and output is a bit tricky. If we use the equation y = mx, then if x = 5, y = 35. That's one possibility. But we could also have x = 6, then y = 42.
Hope this helps.