Solve each system of elimination.
a.)
x+7y=16
-8x+3y=-10

b.)
y=4
2x+6y=18

For A)

multiply the top equation by -8 to match up your first terms and cancel them out through subtraction:

-8x - 56y = -128
- (-8x + 3y = -10)

so your x variable is eliminated
-8x - - 8x = 0

-59y = -118 ... divide both sides by -59
y = 2

take your y variable result and plug it back into an equation, then solve for x:
-8x + 3(2) = -10 ... multiply 3 and 2
-8x + 6 = -10 ... combine like terms
-8x = -16 ... divide by -8
x = 2

your solutions are (2, 2)

B)
y = 4
2x + 6y = 8

why they would ask you to do this by elimination when substitution is worlds easier, we don't know, but regardless you want to match the y variables up since it's the only variable you have.
6y = 24
- (2x + 6y = 8)

so your y terms cancel out:
-2x = 16 ... divide by -2
x = -8

and to check your y variable, plug x back in to your equation:
2(-8) + 6y = 8
-16 + 6y = 8
6y = 24
y = 4 is correct

so your y variable was given, but still: (-8, 4) is a solution