In the 2018 Test 4 a question asks to show that the standard 3 year swap rate is 6.45% if we have the following 12 month forward rates: Year 1: 5%, Year 2: 7%, Year 3: 7.5%.

In finding the answer they solve for \(i\) such that \(5v+7v^2+107.5v^3=100\). Why do they do this? To me, it would make sense to solve for \(x\) such that

$$5v_{5\%}+7v_{7\%}v_{5\%}+7.5v_{7.5\%}v_{7\%}v_{5\%} = x(v_{5\%}+v_{7\%}v_{5\%}+v_{7.5\%}v_{7\%}v_{5\%})$$

Am I misinterpreting the question?