Solve the simultaneous equation: 3x+y =-4 and 3x-4y=6

The first step would be to rearrange the first equation to make y the subject:
3x+y=-4 ----> y=-4-3x
Next we want to substitute this value of y into the second equation
3x-4y=6 -----> 3x-4(-3x-4)=6
Next we should multiply out the brackets and rearrange.
3x+12x+16=6 ---> -15x+16=6 ----> 15x=-10
Now divide both sides by the multiplier (15) to find the value of x
x=-10/15 ----> x=-2/3
Substitute the value of x into the equation we originally rearranged to find y
y=-4-3x ------> y=-4-3(-2/3) -----> y=-4+2 ----> y=-2
To make sure the values you have are correct, substitute the values into the second equation to ensure the answer is 6.
3x-4y=6 ----> 3(-2/3)-4(-2)=6 ----> -2+8=6 ----> 6=6
Hence x=-2/3 and y=-2