Ron, You Said:
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"R= P+P*I*T
Factor out P ‘algebra’.
R= P*(1+I*T).
R= $298*(1+.0195*15.4166).
R= $387.58 Billion.
Now add back in valuation for WMB of $298 Billion
$685.59"
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Sorry, BUT your Math has a Mistake....
You are right as far as the Formula of "R" BUT 'R" is the Actual TOTAL Amount, that INCLUDES the Principal + The 'Return" on that Principal for that Interest Rate 'I".
So, TOTAL Amount is $387.58B and You Should NOT Add Back the "Principal' of $298B again!
TIA & GLTU & GLTA!