Answer:
153.94 in²
Step-by-step explanation:
X = large boxes and y = small boxes
x + y = 70.....x = 70 - y
60x + 65y = 4300
60(70 - y) + 65y = 4300
4200 - 60y + 65y = 4300
5y = 4300 - 4200
5y = 100
y = 100/5
y = 20 <=== the small boxes weigh 20 lbs
x + y = 70
x + 20 = 70
x = 70 - 20
x = 50 <== and the large boxes weigh 50 lbs
The volume of a rectangular prism is represented by the following equation:

Where the variables are for volume, width, height, and length, respectively.
We are given that the area of one end is 16 cm² (units have to be correct when solving these problems, so it's 16 cm², not 16 cm as described in the problem). We know that 
Using this knowledge, we can change the volume equation to our needs.



Note: We know that A is 16 since it's given

The volume is 208 cm³ (once again, incorrect units given). Insert this into the equation.

Divide both sides of the equation by 16.

The length is 13 cm.
Let me know if you need any clarifications, thanks!