Question 1176917
It helps to draw this.
the paper is in pieces x and 2x
the 2x is divided in a 3:4 ratio and the resulting pieces are (6/7)x and (8/7)x to make a 3:4 ratio--(2x/7)*3 and *4.
The shortest piece of the three is (6/7)x, so the difference is (8/7)x-(6/7)x=(2/7)x=12 cm. 
x=42 cm
2x=84 cm
the answer is the sum or 126 cm
the 84 cm length side is divided up into 36 cm and 48 cm sizes.