1. **Problem statement:** Evaluate the expression \n\na) \n$$\frac{2 \frac{2}{3} - \frac{5}{6}}{\frac{2}{3}}$$\n\n2. **Convert mixed number to improper fraction:** \n$$2 \frac{2}{3} = \frac{3 \times 2 + 2}{3} = \frac{8}{3}$$\n\n3. **Rewrite the numerator:** \n$$\frac{8}{3} - \frac{5}{6}$$\n\n4. **Find common denominator for subtraction:** \nThe common denominator of 3 and 6 is 6. \nRewrite $\frac{8}{3}$ as $\frac{16}{6}$. \n\n5. **Subtract fractions:** \n$$\frac{16}{6} - \frac{5}{6} = \frac{16 - 5}{6} = \frac{11}{6}$$\n\n6. **Divide by $\frac{2}{3}$:** \n$$\frac{\frac{11}{6}}{\frac{2}{3}} = \frac{11}{6} \times \frac{3}{2}$$\n\n7. **Multiply fractions:** \n$$\frac{11}{6} \times \frac{3}{2} = \frac{11 \times 3}{6 \times 2} = \frac{33}{12}$$\n\n8. **Simplify fraction:** \n$$\frac{33}{12} = \frac{\cancel{33}}{\cancel{12}} \text{ (no common factors except 3)}$$\nDivide numerator and denominator by 3: \n$$\frac{33 \div 3}{12 \div 3} = \frac{11}{4}$$\n\n9. **Final answer for part a:** \n$$\frac{11}{4} = 2.75$$\n\n---\n\n1. **Problem statement:** Evaluate the expression \n\nb) \n$$\frac{1.68}{1.5^2 - 1.45}$$\n\n2. **Calculate denominator:** \n$$1.5^2 = 1.5 \times 1.5 = 2.25$$\n\n3. **Subtract:** \n$$2.25 - 1.45 = 0.8$$\n\n4. **Divide numerator by denominator:** \n$$\frac{1.68}{0.8} = 2.1$$\n\n5. **Final answer for part b:** \n$$2.1$$