using the LCD method.... well, there are a couple of ways, but let's simply add them up.
well, the denominators are 5x and 2x... so the only LCD will just be 10x, since it's divisible by both, so let's use that one.
[tex]\bf \cfrac{2}{5x}+\cfrac{7}{2x}=1\implies \stackrel{\textit{LCD of 10x}}{\cfrac{(2)2~~+~~(5)7}{10x}}=1\implies \cfrac{4+35}{10x}=1\implies \cfrac{39}{10x}=1 \\\\\\ 39=10x\implies \cfrac{39}{10}=x\implies 3\frac{9}{10}=x[/tex]
