The question reads, " express each of the following quantities using significant figures to imply the stated error".
a) $2.3 \pm 0.001$
b) $1.989 \pm 0.0003$
I think the first one is 2.300 because the zero in the thousands place implies an error of $\pm0.001$ but how do I use sig figs to imply an error of $\pm 0.0003$?
Your a) sounds good to me. For b) I think you have to divide by 3: $$ 1.989 \pm .0003 = 3(.663\pm .0001)$$ So you'd short-hand that as $3*.6630$.
Which is kind of weird to me, but I don't see how else to make sense of the problem.