Our original value is $1,800. Every 7 years that value doubles, so at 7 years, our value would be $3,600. At 14 years, the value would be $7,200. At 21 years, the value would be $14,400. At 28 years, the value would be $28,800. At 35 years, the value would be $57,600. At 42 years, the value will be $115,200.
I hope this helps!
