I got 18. I first multiplied the second by 2 to get 8H+ and cancel those out. Then I did the new second equation by 2 to get 4H2O and cancel those out.

Then I had to divide by 2 to get 8e- and multiply the first one by 8 and the second one by 5 to cancel out 40e-

I ended up with products side coeffiecients as 18. Do you think the book made an error? No text is perfect. I have caught some errors in it.

After multiplying add both reactions by sides and calculate H+ on the left side and water on the right one