3x +6y=21 and -5x+2y=13

First, let's solve the first equation for one variable:

3x + 6y = 21
3x = 21 - 6y
x = (21 - 6y) / 3
x = 7 - 2y

Now, substitute this expression for x into the second equation:

-5(7 - 2y) + 2y = 13
-35 + 10y + 2y = 13
12y = 48
y = 48 / 12
y = 4

Now that we have found the value of y, we can substitute it back into the expression we found for x in the first equation:

x = 7 - 2(4)
x = 7 - 8
x = -1

Therefore, the solution to the system of equations is x = -1 and y = 4.