How long is the unpainted strip of each part of the road

208 yard divided by 16 = 13 parts

if he paints 4 yards in each 13 parts he just needs to paint 9 more yards.

the answer is 9 yards

1 number

if we use a graphing calculator, there is only one such number that satisfies the conclusion of the mean value theorem, that is, a number such that

where the right-hand side is the average rate of change of f on the interval [0.5,0.75], which is the slope of the secant line.

in the attached graph, the black line is the secant line which has its slope as the average rate of change of f on [0.5,0.75], while the orange line is the only tangent line to the graph of f in the interval that satisfies the mvt conclusion.

or