You can use what you know about equivalent ratios and operations with fractions to write a ratio of fractions as a unit rate.

Tia skateboards 2/3 mile for every 1/6 hour.

(2/3) / (1/6) = [(2/3) × (6/1)] / [(1/6) × (6/1)] = 4/1 = 4

She skateboards 4 miles per hour.

[Ratio table: Miles 2/3 → 4; Hours 1/6 → 1; multiply both by 6.]