Because this isn't an equation we can't simply multiply through by the lowest common denominator to get rid of the fractions. But what we can do is what we would do in arithmetic. We still use the LCD and we separate the numerator by a line over the denominator.
Assuming the question is meant to read: ((x^2)/5-x/5-3/4)+((x^2)/10-x/2+1/2) we have LCD=20.
Multiply the expression through by 20 and divide it all by 20: ((4x^2-4x-15)+(2x^2-10x+10))/20.
We can open the inner brackets to make it easier to combine the terms: (6x^2-14x-5)/20. This doesn't factorise rationally so this is as far as we go. However, you could divide each term by 20: 3x^2/10-7x/10-1/4. Or even decimalise it: 0.3x^2-0.7x-0.25.