Step-by-step explanation:
I guess, it means every meter costs these amounts.
and the specified costs are not fit the whole bundle.
it is also unclear, if "half of it" means half of the original x meters, or half of the remaining meters (after selling 2/5 of the original meters). I assume the first.
so, we have
-5x
+ 2/5x × 5.5
+ 1/2x × 6.4
+ (10/10 - 4/10 - 5/10)x × 6 = + 1/10x × 6
= 120 ( a income minus costs is the profit, so balancing both sides in a "+" and "-" expression gives us the remaining profit).
about the line with the 1/10 :
the leftovers. 10/10 is the whole x at the beginning.
2/5 = 4/10.
1/2 = 5/10.
I brought all involved fractions to the same denominator of the smallest common multiple of 2 and 5 (10).
in full
-5x + (2/5)x×5.5 + (1/2)x×6.4 + (1/10)x×6 = 120
-5x + 2.2x + 3.2x + 0.6x = 120
-5x + 6x = 120
x = 120
so, he bought 120m in the first place.
