Answer:
okay so, everytime you see anything that says "a number", that will automatically mean that there is a number in the equation that u dont know, so instead of putting a random number in its place, you put an "exponent" aka a letter like "x" for example. so it says, 12 is the sum of a "number" and 3, that means 3 plus a number gives u 12, you would have to make an equation to find the "number" so the equation would be "3 + x = 12".
Explanation: