If the ratio is 5:7 then the each part has a value of:
60/(5+7)=5 so from a total of 60
5:7 becomes 5*5:7*5 which is:
25:35
-5.8 - (-8.4)
When we multiply two negatives they become a positive. In this situation, where there is no other number, you can assume there's basically a 1 in that place.
-5.8 - 1(-8.4) would be just as correct. (If this helps visually clarify anything.)
So we take that -1 and multiply it by that -8.4. Multiplying 1 against anything leaves it the same, so we just need to change the sign. Two negatives make a positive.
-5.8 + 8.4
Now we add these together.
This gives us our final answer of 2.6