**Q3: **

If , what is the value of ?

**Q4: **

If , what is the value of ?

**Q5: **

Solve the following equation mentally: .

**Q6: **

Solve the following equation mentally: .

**Q7: **

Solve the following equation mentally: .

**Q8: **

Solve the following equation mentally: .

**Q9: **

Solve the following equation mentally: .

**Q10: **

Solve the following equation mentally: .

**Q11: **

Solve the following equation mentally: .

**Q12: **

Solve the following equation mentally: .

**Q13: **

Solve the following equation mentally: .

**Q14: **

Solve the following equation mentally: .

**Q15: **

Solve the following equation mentally: .

**Q16: **

Solve the following equation mentally: .