AB and PQ are lines of length 6cm

AX:AB=1:3 mark where point X would be on the line with a cross

To mark point X on the line AB with the ratio AX:AB = 1:3, divide the line AB into four equal parts. Start from point A and mark a point 1.5 cm away. Then, continue marking points every 1.5 cm until you reach the end of the line AB. The fourth point you mark will represent point X.