Solving for 3 variables questions :o help!
Solve the system by elimination 1: x+5y-4z=-10, 2x-y+5z=-9, 2x-10y-5z=0 .
2. Solve the system by substitution: 2x-y+z=-4, z=5, -2x+3y-z=-10.
3. A food store makes a 11–pound mixture of peanuts, almonds, and raisins. The cost of peanuts is $1.50 per pound, almonds cost $3.00 per pound, and raisins cost $1.50 per pound. The mixture calls for twice as many peanuts as almonds. The total cost of the mixture is $21.00. How much of each ingredient did the store use?

Question

Solving for 3 variables questions :o help! 
Solve the system by elimination 1: x+5y-4z=-10, 2x-y+5z=-9, 2x-10y-5z=0 . 
2. Solve the system by substitution: 2x-y+z=-4, z=5, -2x+3y-z=-10. 
3. A food store makes a 11–pound mixture of peanuts, almonds, and raisins. The cost of peanuts is $1.50 per pound, almonds cost $3.00 per pound, and raisins cost $1.50 per pound. The mixture calls for twice as many peanuts as almonds. The total cost of the mixture is $21.00. How much of each ingredient did the store use?

anonymous · Answer

options for the 1st one are :     (5, –1, 0)
    (–5, 1, 0)
    (–5, –1, 0)
    (–5, –1, –2)

Options for the second are:     (–8, 7, 5)
    (–8, –7, 5)
    (8, –7, 5)
    (–8, –7, –5)

And the 3rd :    3 lbs peanuts, 6 lbs almonds, 2 lbs raisins
    8 lbs peanuts, 1 lb almonds, 2 lbs raisins
    6 lbs peanuts, 3 lbs almonds, 2 lbs raisins
    8 lbs peanuts, 2 lbs almonds, 1 lbs raisins