Remember, you take 1/2 of b and square it to get c
c=100
(b/2)^2=c
(b/2)^2=100
sqrt oth sides
b/2=+/-10
times both sides by 2
b=+/-20
it is 20 or -20
answe ris B
yo is right
Is there more to this problem? By saying f(4), you'd be inputting a 4 for every variable x. There is not enough info here to answer the question.
the formula for slope is

so just replace y and x for the proper values
B, x=12 because 140-80=60, 60/5=12