When you are asked to solve an equation, you need to isolate the variable which is t in this case. To isolate t, you would divide both sides by -5 and be left with t=-6 which is the final answer.
I hope this helps.
Let the slower cars speed equal X.
The faster cars speed would be X+5 ( 5 mph faster).
They traveled for 3 hours
Multiply the time of travel by speed to equal the number of miles traveled.
So you have:
3X + 3(X+5) = 267 miles
Simplify the left side:
3X + 3X+15 = 267
Combine like terms:
6x + 15 = 267
Subtract 15 from each side"
6x = 252
Divide each side by 6:
x = 252 / 6
X = 42
The slower car was traveling at 42 mph and the faster car was traveling at 47 mph.