Let t be the tens digit and u be the ones digit. Then from the condition, we have two independent equations t - u = 4 (1) t = 2u - 1 (2) Substitute t from (2) into (1). You will get (2u-1) - u = 4, or u = 5. Then from equation (2), t = 2*5-1 = 9. ANSWER. The number is 95.