[tex]\frac{x}{5} - \frac{x}{2} = 21[/tex]
We need a common denominator to subtract. Easiest way to do this is to find the LCM for both denominators. The number 10 will work since both 5 and 2 are multiples of 10 and 10 is LCM is 10 and 2.
[tex]\frac{x}{5} - \frac{x}{2} = 21[/tex] =>
[tex]\frac{2x}{10} - \frac{5x}{10} = 21[/tex]
Subtract normally.
[tex]\frac{2x}{10} - \frac{5x}{10} = 21[/tex] =>
[tex]\frac{-3x}{10} = 21[/tex]
Multiply each side by 10
[tex]\frac{-3x}{10} = 21[/tex] =>
[tex]-3x = 210[/tex]
Divide both sides by -3
[tex]-3x = 210[/tex] =>
x = -70
The correct answer is A.
