EPC4 1.5.41
Hint: Δt in years is the fraction of the year, so S(t) Δt is the approximate income during this time interval, 12 percent of which contributes to ΔA, while the interest contribution is the annual interest rate 6 percent prorated by multiplying by the fraction Δt for the interest contribution over this shorter time period, applied to the current value of the retirement amount A(t): 6 percent of A(t) Δt; adding these and dividing by Δt, taking limit to get dA/dt gives the linear DE
If you have trouble setting up the DE after this hint which should enable you to go directly to the DE, only then punt and use the dsolve template to solve this DE (click on "this DE"!) with its initial condition; evaluate answer to question of word problem to a floating point number and give the result in dollars and cents in a comment, then think about significant figures and give a response with fewer significant digits.
If you have a viable future which is not clear from the present political and environmental chaos, you will need to worry about saving for retirement, so this is not just an artificial math problem.