Use the Pythagorean theorem to find the length of the diagonal, or the hypotenuse of an imaginary triangle. 30^2 + 40^2 = 2500, which is 50^2. So, the magnitude is 50.
A "fixed price" energy tariff means that your unit price for gas and electricity will not change for the duration of the plan. A variable rate means your energy price can vary during the plan. If you have a fixed price plan and your supplier announces a price rise, your rates will not change.
