Joe is told by his ophthalmologist that he requires glasses with a refractive power

Joe is told by his ophthalmologist that he requires glasses with a refractive power of −4.50 d to correct his vision. his previous prescription was −4.00 d. (a) is joe nearsighted or farsighted? (b) when joe is not wearing his glasses, how far away can he see objects clearly? (c) when he wears his old prescription, how far away can he see clearly?