Let r be speed going to dallas
let t be time going to dallas
Other known given variables
Generalized data table according to variables described
speed time distance
TO r t d
FROM r+j t-k d
Uniform Travel Rate rule works like RT=D relating speed, time, distance. You want to form a system of equations and solve for the value of r, or a formula for r and then evaluate.
System should be, if keeping all in symbols,
Working through the system, you should obtain , from which you can get a formula for r. (You may also find that substituting the given values into the quadratic equation now may give a fairly easy equation to deal with or maybe/maybe-not factorize).
Substituting for the given numbers now and simplifying in fact gives the quadratic . Go from that.
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Formula for general solution for quadratic equation will accordingly give
, the PLUS-form.