-3/2+3/-5

-3/2= -1.5

3/-5 = -0.6

-1.5+-0.6=-2.1 

$-\dfrac{3}{2}+\dfrac{3}{-5}$

=$-\dfrac{15}{10}-\dfrac{6}{10}$

=$\dfrac{(-15-6)}{10}$

=$-\dfrac{21}{10}$