What is the slope of the street line through points (2,10) and (5,8)

Y=mx+b is the equation of a linear function, which is what this question is asking.

since you have 2 points, you can use this equation for solve for "m", the slope

y2-y1/x2-x1

this would be 10-5/8-2 in this case, which is 5/4
you now have 5/4 as your slope
you can then take one of your points, and substitute in for the original y=mx+b equation
8 = 5/4 * 5  + b
8 = 25/4 + b                multiply the fractions together (multiply across)
32 = 25 + b     (multiply both sides by 4 to eliminate the fraction
7 = b         ( subtract 25 from both sides )