Explain how you would know that the following system has an infinite number of solutions, without solving it. y = 2x + 5 -4x + 2y = 10

There aren'y many cubes below 36. The only three possibilities are 1, 8, 27.

Similarly, the factors of 20 are 1, 2, 4, 5, 10, 20.

Now, let's dive through the possible cases: if the cube number is 1, we need two factors of 20 that sum up to 35. This is not possible, since the sum of the two largest, 20 and 10, is only 30.

If the cube number is 8, we need two factors of 20 that sum up to 28. This is not possible, because there's not way to choose two numbers such that the sum of the unit digits is 8.

So, the cube number must be 27. We deduce that the other two numbers, the factors of 20, must sum up to 9. The choice is clearly 4 and 5.