(6 - 2 / (1/10 2/1 / 7)) 4/15
(6 - 2 / (0.1 0.2857)) 4/15
(6 - 2 / 0.02857) 4/15
(6 - 69.86) 4/15
(-63.86) * 4/15
-15.9433333...