For year $2022,$ a company reports net operating profit after taxes $($NOPAT$)$ of $$32,910\mathrm{.}4$ million. The following additional information is gathered from its financial statements $($in millions$)$:

End of $2022$ End of $2021$

Operating assets $$337,052\mathrm{.}7$ $$388,934\mathrm{.}1$

Nonoperating assets $$18,916\mathrm{.}9$ $$20,649\mathrm{.}9$

Operating liabilities $$85,432\mathrm{.}7$ $$98,300\mathrm{.}2$

Nonoperating liabilities $$170,865\mathrm{.}6$ $$196,600\mathrm{.}0$

a$.$ Assuming a weighted average cost of capital of $7\mathrm{.}0\%,$ what was the company$$s residual operating income $($ROPI$)$ for year $2022?$

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b$.$ At what level of WACC would the company not report positive ROPI? In other words, what value of WACC would cause expected NOPAT to equal actual NOPAT?

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