You have that Marilyn earns a monthly salary of $3,400.
In order to calculate the yearly earnings, you consider that one year has 12 moths. Each month Marilyn earns $3,400, then, to find the yearly earnings you multiply monthly earningg by the number of months in one year. Just as follow:
yearly earnings = ($3,400)(12) = $40,800
Hence, Marilyn earns a yearly salary of $40,800