-3.
Multiply 60 with 4 and then find the factor when added together which would give you the middle number. Notice that because it is a negative equation that both signs are negative. This means that the biggest factor of 240 will be negative.
Then, rewrite the equation 4x^2 +12x -20x -60 and divide it into two parts (4x^2 + 12x) (-20x-60) and then factor each part. If done correctly, the numbers left in the parenthesis should be the same. This way the part outside is one factor and the part inside is the other. This should get you 4x -20 and x +3.
Set both equal to zero and you get your two solutions. One is -3 and the other is 5.
Hope this helps!
By answering the question and reading the question
V1=50km/h
v2=90km/h
s1=s2=6km
s=12km
The average speed over the 12 km drive:
v=s/t
The time needed to drive 12km will be:
t = t1+t2
t1=s1/v1, t2=s2/v2
t=s1/v1+s2/v2=(s1v2+s2v1)/(v1v2)
v=sv1v2/(s1v2+s2v1)=12*50*90/(6*50+6*90)=64,28 km/h
