How are you meant to find out the total resistance if you don't have a voltmeter reading and how are you meant to find out the volt meter reading if you don't have a total resistance?

Solve for resistance using power and current.
Substitute IR for V in the first formula: P = (IR)I = I2R. Rearrange to solve for resistance: R = P / I2. In a series circuit, the current across one component is the same as the total current. This is not true for a parallel circuit