Matt collects classic stamps. For his birthday this year his grandma gave him a stamp’s worth $40. He expected the stamps value to double every decade. Assuming Matt is right you can use a function to approximate the stamp’s value x decades from now.
Write an equation for the function. If it is linear write in the form h(x)=mx+b. If it is exponential, write it in the form h(x)=a(b)^x