6. (30 points) The value of the Brazilian real (R$) has changed substantially against the U.S. dollar in recent years. For example, the reals-per-dollar exchange rate has moved from R$3.20/$ on Aug 15th, 2017 to R$4.01/$ on Aug 15th, 2019, and then later to R$5.25/$ on Aug 15th, 2021. (a) By what percentage did the value of the Brazilian real change during the first two years of this period (against the dollar)? (b) By what percentage did the value of the dollar change during the first two years of this period (against the real)? [i.e. from 8/15/17 to 8/15/19] (c) By what percentage did the value of the Brazilian real change during the latter two years of this period (against the dollar)? (d) By what percentage did the value of the dollar change during the latter two years of this period (against the real)? [i.e. from 8/15/19 to 8/15/21] (e) By what percentage did the value of the Brazilian real change during the entire four-year period (against the dollar)? (f) By what percentage did the value of the dollar change during the entire four-year period? (against the real)? [i.e. from 8/15/17 to 8/15/21]