78=-6(8k-9)-12(k+6)
78 = -6(8k - 9) - 12(k + 6)
Use the distributive property:
78 = -48k + 54 - 12k - 72
Simplify:
78 = -60k - 18
Add 18 to both sides:
96 = -60k
Divide by -60 and reduce:
k = 96/-60 = -8/5