Certain pieces of antique furniture increased very rapidly in price in the 1970s and 1980s. For example, the value of a particular rocking chair is well approximated by $$V = 70 (1.55)^t,$$ where $V$ is in dollars and $t$ is the number of years since 1975. Find the rate, in dollars per year, at which the price is increasing.

rate = dollars/yr