Chapter 1 - Measurement and Problem Solving - Learning Path Questions and Exercises - Exercises - Page 30: 36

$6.1 cm/year $ (Rounded off)

$5ft 6 inch=5\times 12 +6 = 66 inch$ At age 20, her height is 66 inch, At age 0 , her height was 18 inch. So, increase in height = $66-18=48 inch$ Average rate of growth = $\frac{48}{20}=2.4 inch\, per\, year= 2.4 \times 2.54 cm\, per \,year= 6.1 cm/year. $ (rounded off)