I don’t know it tried solving it but couldn’t find it

8f - 25 = 47. Add 25 to both sides.

8f = 72. Divide each side by 8.

f = 9.

f = 9

Step-by-step explanation:

8f - 25 = 47

Add 25 to both sides.

8f - 25 + 25 = 47 + 25

On the left side, -25 + 25 = 0, so the -25 is eliminated.

On the right side, we add 47 + 25 = 72

8f = 72

Now we divide both sides by 8.

8f divided by 8 is just f. 72 divided by 8 is 9.

f = 9

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.