Generalized arithmetic allows you to state things like the commutative property of addition: a + b = b + a. Or the property that when you add zero to a number, you get the same number: 0 + n = n. Or the property that the product of two square numbers is a square number: x2 * y2 = (x * y)2.
The answer is n = 4. One method is the patented "guess-and-check." Others include systematic testing of values of n starting with n = 1, or "undoing" the operations on the left sidečif we have to multiply n by 9, then add 4, a way to find n would be to subtract 4, then divide by 9.
Some situations include the relationship between the length of a side of a square and the square's area (A = s2), the relationship between Fahrenheit and Celsius temperature (F = 1.8C + 32), and the relationship between distance, rate, and time (D = r * t). In all of these, the variables vary and represent relationships between two or more quantities.