It takes nora two hours to paint a wall 5m by 8m, and zack three hours to paint a wall 4m by 9m. together, how long will it take them to paint a wall 10m by 12m?

check the picture below.

well, the angle at the vertex d is clearly not a right-angle, let's check for the one at the vertex f which does look like,   however if it's indeed, that means ef is perpendicular to df, in which case their slopes will be negative reciprocal of each other.

so the negative reciprocal of the slope of ef is 1, however the slope of df is not 1, is 1/2, so nope, they're not perpendicular lines.

step-by-step explanation: yes