Answer:
time require is 2.3 years
Explanation:
given data
currently costs = $28,000
inflation rate = 6%
effective annual return = 10%
future value = $40,000
solution
first we get here interest rate that is
interest rate = annual return investment + inflation rate + ( annual return × inflation rate ) .......................1
put here value and we get
interest rate = 0.10 + 0.06 + ( 0.10 × 0.06 )
interest rate = 0.166
and now we get here present value that is express as
future value = present value ×
.....................1
put here value and we get
present value =
28000 = 
0.7 = 
take log both side we get
log( 0.7) = -t log (1.166)
solve it we get
t = 2.3 year
so time require is 2.3 years