The standard error of the mean has the formula where (greek letter sigma) is the standard deviation and n is the sample size.
As n gets bigger, the standard error gets smaller, and vice versa. This assumes sigma is fixed. A larger sample indicates the error goes down to narrow in better on the population mean.
Based on what I mentioned, this tells us that sample A has the larger standard error since n = 350 is smaller than n = 500 for sample B.
Algebracicaly speaking the answer would be either -13.3876 or - 158.612 through the quadratic equation, but these answers don’t make sense in this real world scenario.