2/5x=-8/15

2/5 x = -8/15

Divide both sides by (2/5) to isolate x: 

x = (-8/15) / (2/5)

$${\frac{{\mathtt{\,-\,}}\left({\frac{{\mathtt{8}}}{{\mathtt{15}}}}\right)}{\left({\frac{{\mathtt{2}}}{{\mathtt{5}}}}\right)}} = {\mathtt{\,-\,}}{\frac{{\mathtt{4}}}{{\mathtt{3}}}} = -{\mathtt{1.333\: \!333\: \!333\: \!333\: \!333\: \!3}}$$

x = -4/3