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The 1st and 3rd choices are irrational. The other 2 are rational. Irrational numbers are numbers that you can't make a simple fraction out of.
Since both have same speed
v(rel.) x-(-x)= 10( from law of vector addition)
2x=10,x= 5m/sec
The smallest possible number for the third side would be 15
The area of the top of the plate is 25 square inches