A driver is going 23$\mathrm{}\mathrm{}$ m/$/$s when she sees a sign ahead with a speed limit of 12$\mathrm{}\mathrm{}$ m/$/$s.$.$ The sign is only 53$\mathrm{}\mathrm{}$ m in front of her. What magnitude ($($absolute value, no negative sign)$)$ of acceleration does she need to slow to the posted speed limit in time? Enter your numerical answer in m/$/$s^{2$\mathrm{}$ .}