Division in algebraic equations can be confusing. When you throw x's and n's into an already difficult type of math, then the problem may seem even more difficult. By taking a division problem apart piece by piece, however, you can reduce the complexity of the problem.
Copy your equation on a separate sheet of paper. For the first example, use 3n/5 = 12.
Begin by isolating the variable (n). In this equation, the first thing is to remove the /5. To eliminate division, you do the opposite operation -- which is multiplication. Multiply both sides of the equation by 5. (3n/5) * 5 = 12 * 5. This gives 3n = 60.
Isolate the variable by dividing by 3 on both sides of the equation. (3n/3 = 60/3). This gives n = 20.
Check your answer. (3*20)/5 = 12 is correct.
Solve more complex equations in the same manner. For example, (48x^2 + 4x -70)/(6x -7) = 90. The first goal is to isolate the variable. This requires simplifying the left hand side of the equation.
Factor the numerator and denominator of the equation completely. In this equation, the denominator is already simplified. You need to factor the numerator. The numerator factors into (8x + 10) (6x - 7).
Cancel the common factor. The 6x - 7 on the numerator and the 6x - 7 on the denominator cancel each other. This leaves 8x + 10 = 90. Solve for x by subtracting 10 from both sides and dividing by 8. You end up with x = 10.
Check your answer. (48 * 10^2 + 4 * 10 - 70)/(6 * 10 - 7) = 90. This gives you 4770/53 = 90, which is correct.