I need help! Calculating relative frequency?

A form of albinism in humans occurs at a frequency of 9 of 10,000 infants born in a particular country (i.e., 9 x 10-4, or 0.0009. This form of albinism is due to a recessive allele (a) and individuals that are albino are genotype aa. What is the relative frequency of heterozygotes (“carriers”) in this population (round to the nearest 0.01)?