Why won't it give me full marks for this? What have I missed?
The question is from Mathswatch.

Which function is represented by the graph

Select the correct answer from each drop-down menu. rewrite the formula to find voltage. the formula for electrical power (p, in watts) is where v is the voltage in volts and r is the resistance in ohms. for a particular brand of water heater, r is 32 ohms and p is 0.5 watts. the formula to find v is , and the voltage at which the heater operates is volts.

What is the number 321,000,000 in scientific notation? also what is the number? ?