7-4x= 31
Bring over 7 to the other side
Positive 7 changes into negative 7
7-7-4x= 31-7
-4x= 24
Divide by -4 for -4x and 24
-4x/-4= 24/-4
x= -6
Check answer by using substitution method
7-4x= 31
7-4(-6)= 31
7+24= 31
31= 31
Answer : C. x= -6
2 * plane speed in still air = 289mph + 257mph = 546
plane speed in still air = 273 mph
plane speed in still air + wind speed = 289
273 + wind speed = 289
Therefore, wind speed = 16 mph
