Which variable to use for initial conditions?

Please add: "solve for the top" to the instructions in this video. Namely given dx/dt, think of "x on top", "t on the bottom." Plan is to ultimately solve for x. The initial conditions will be presented for example as: N(7 ) = 2. When you substitute, let the bottom, here t= what's in the ( ), here 7. Let the top, here x = the opposite side of the equal sign, here 2. Therefore when substitute, let t = 7, x = 2 and ignore the N and solve for x.