Excerpts recommend spending 25-28% of your total monthly income on housing. What percentage of their income do Henry and Claire pay for housing (mortgage, taxes, and insurance)?

  16.4 million viewers

Step-by-step explanation:

The number of viewers increased by 8 million from 10 to 18 million when the number of ads increased by 10 ads from 15 to 25. If 23 ads are run, that represents an increase of 8 ads from 15, so we expect 8/10 of the increase in viewers.

  8/10 × 8 million = 6.4 million

The number we expect with 23 ads is 6.4 million more viewers than 10 million viewers, so is 16.4 million.

Alternate solution

We can write a linear equation in 2-point form for the number of viewers expected for a given number of ads:

  y = (18 -10)/(25 -15)(x -15) +10

  y = (8/10)(x -15) +10

  y = 0.8x -2 . . . . . million viewers for x ads

For 23 ads, this gives ...

  y = 0.8×23 -2 = 18.4 -2 = 16.4 . . . . million viewers, as above

Comment on 8/10

I consider it coincidence that the number 23 is 8/10 of the difference between 25 and 15, and the slope of the line is 8/10. The point we're trying to interpolate has no relationship to the slope of the line, and vice versa.