Answer: The expression factors to (2x - 1)(5x + 4)
In a rectangle the area is L x W. So if we know the area is 10x^2 + 3x - 4, then all we have to do is factor it to find possible values for the L and W.
If you factor the expression by grouping, you will get (2x - 1) and (5x + 4).
Your questions asks for possible dimensions, you could give the two expressions as dimensions.
If you wanted to select a value for x, you could plug it in and get values that could be dimensions.
For example if you let x = 10, you would have a rectangle that has a width of 19 and a length of 54.