so this is ratios
actual height to shadow height=10 to 18=10:18=10/18=5/9
ratio is 5:9
if the shadow height=12 then find actual height
x:12=5:9 since they should be in the same ratio
x/12=5/9
multiply both sides by 12
x=60/9
x=6 and 6/9
x=6 and 2/3
height of person is 6 and 2/3 foot or 6.66ft or 6ft and 8 inches