Reading 10, Problem 13 only, understand, computing, question, schedule

Wasteoftime

This question pertains to 13.A.ii specifically.

I was wondering how they arrived at the after-tax 4.427 percent, given that the Maclins live beyond their means with an annual outflow of 26,000. I understand the arrival of the Investable Asset Base of 1,235,000, and even tried a CF schedule with N=18, PV= 1,235,000 FV=2,000,000 PMT=-26,000 and computing I/Y only yields an Error 7 message.

Any thoughts, besides manually calculating each outflow and return for all 18 years?

Thanks!