2t + 3 = -9 lets us solve for t by isolating the variable. first we can subtract 3 from both sides to get rid of it on the left side of the equation. That gives us 2t = -12. Then we can divide by 2 to isolate t completely. Now we have t = -6.
We can use this in the 2nd equation to just plug in t. -3t - 7 = -3(-6) - 7. We multiply -3 and -6 and get 18 because the negatives cancel out when multiplying 2 negative numbers together. The equation is now 18 -7 which is equal to 11.
