400 - 2x = 244
-2x = 244 - 400
-2x = -156
x = -156 / -2
x = 78
a) 
The average speed is equal to the ratio between the total distance (
and the total time taken (
):

the distance travelled by the trucker in the first 3 hour can be written as the time multiplied by the velocity:

So the total distance is

The total time is equal to the first 3 hours + the time taken to cover the following 20 miles in the city:

So, the equation can be rewritten as:

b) 0.50 h (half a hour)
Since we know the value of the average speed,
, we can substitute it into the previous equation to find the value of
, the time the trucker drove in the city:

Answer: 45b^4/32
Step-by-step explanation: First multiply the two fractions
15b^3y(3b)/8y x 4
Multiply 3 by 15
45b^3yb/8y x 4
Raise b to power of 1
45(b^1b^3)y/8y x 4
Use power rule to combine exponents
45b^1+3 y/8y x 4
Simplify
45b^4y/32y
Cancel common factor of y
45b^4/32
Answer:
B)6v3; 12
The answer to the question is b.