In order to determine the weighs of the boxes, name x as the larger box and y as the smaller one.
Then, based on the given situation, you can write the following equations:
3x + 2y = 86
8x + 4y = 209
Solve the previous system of equations as follow:
Multiply the first equation by -2 and add the result to the second equation:
(3x + 2y = 86)(-2)
-6x - 4y = -172
8x + 4y = 209
-6x - 4y = -172
2x = 37
Solve the previous equation for x by dividing by 2 both sides:
x = 37/2
x = 18.5
Next, replace the previous value of x into any of the equations of the system, for instance, into the first equation, and solve for y:
3x + 2y = 86
3(18.5) + 2y = 86
55.5 + 2y = 86
2y = 86 - 55.5
2y = 30.5
y = 30.5/2
y = 15.25
Hence, the weighs of the boxes are:
larger box = 18.5 kg
smaller box = 15.25 kg