tehcnical article – Materials mix and yield variances

Dear John,
I am having trouble understanding the materials yield variance example in the relevant PM technical article.

To calculate the yield variance, I calculated the difference between actual qty of input and st.qty of input for actual production. Then I valued it at the std cost for each input.

The solution in the article calculates the diff between actual output & std. output for actual inputs. Then the variance in physical units is valued at std. cost per unit of output.

When I think about it, the solution in the article makes sense as they have calculated the difference in actual yield vs st. yield for actual input is calculated.

But based on my understanding the method I followed also makes sense, but evidently it is not the correct solution. Could you pls help me figure out the error in my calculation of finding the difference in actual & standard qty of input for actual production, instead of actual output – st. output for actual input).
I am confused trying to figure out how to not repeat this same mistake in other yield calculation question.

Sincerely,
A very grateful student of yours