What is the general rule for differentiation?

In differentiation you multiply the coefficient of the subject (what the value is multiplied by e.g. 3 is the coefficient of 3x⁶) by its exponent (the power that the value is raised to e.g. the exponent of 3x⁶ is 6-) and then reduce the exponent by one. So to differentiate 3x⁶ you multiply 3 by 6 to get a new coefficient of 18, and reduce 6 by 1 to give a new exponent of 5, leaving a final answer of 18x⁵.