Becky and tommy are asked to solve - 4x-25=8x+15 identity where one of them made an error

I feel sorry for Becky and Tommy. The one who didn't come up with x=-10/3 made an error.

first bring 8x to the left and - 25 to the right and simplify:

-4x-8x = 25+15 = > - 12x = 40

x = - 40/12 = - 10/3