Plug in 9 where "a " is. so it reads "6x9+13" then solve. so 6x9=54 then 54+13=67
Let A represent amount of Type A coffee pounds used.
Let B represent amount of Type B coffee pounds used
A + B = 156
B = 156 - A
A = 156 - B
5.80A + 4.65B = 826.60
580 (156 - B) + 4.65B - 826.60 = 0
904.8 - 5.80B + 4.65B - 826.60 = 0
904.8 - 1.15B - 826.60 = 0
78.2 - 1.15B = 0
78.2/1.15 = 1.15B/1.15
68 = B
B = 68 pounds of Type B coffee
There's many more steps you can take to check and etc but am too lazy to put down sorry.
To find the density of the stone divide the mass by the volume:
Density of stone = 100 grams / 10 ml = 10g/ml
Since the density of the stone is more than the density of the water, it will sink.
The first bullet is correct.