The client has asked for some additional support on a particular part of the bridge design - the spotlights - and it would be great if you could support by responding to some of their questions. They want spotlights (streetlights) on the bridge, particularly for reasons relating to safety, but they're also keen to reduce light pollution where they can. They've worked out that they'll need 21 spotlights on each side of the bridge. An option they've been considering is motion-activated lights, which only turn on when they detect activity. Based on initial quotes the client has received, motion-activated spotlights cost more to purchase and install but have lower running costs as they are on for less time. Both motion-activated spotlights and regular spotlights will cost approximately 3 cents to run per hour per spotlight. | II \begin{tabular}{|l|l|} \hline Autumn \& winter months \\ \hline Series & Value \\ \hline Standard spotlights & 360 \\ \hline Motion-activated spotlights & 300 \\ \hline \end{tabular} Spring \& summer months Autumn \& winter months Which of the following ratios most accurately reflects the purchase cost of a single motion-activated spotlight as a proportion of its purchase, installation and running costs over 10 years? 1:2 6:7 4:5 3.5