Question 883075
r/13 = q + 7/13
r = 13q + 7
3r = 3*(13q + 7)
3r = 3*(13q) + 3*(7)
3r = 39q + 21
3r/13 = (39q + 21)/13
3r/13 = 39q/13 + 21/13
3r/13 = 39q/13 + 21/13
3r/13 = 3q + 21/13
3r/13 = 3q + (13+8)/13
3r/13 = 3q + 13/13 + 8/13
3r/13 = 3q + 1 + <font color="red">8</font>/13


So the remainder is <font color="red">8</font>