t is equal to -18.7.
You can find this by getting all the t values to the left side and all the number values to the right. The work is done below for you.
-4.48 - 17.8t + 10.29 = -12.89 - 18.8t -----> Add 18.8t to both sides
-4.48 + t + 10.29 = -12.89 ----> Subtract 10.29 from both sides
-4.48 + t = -23.18 -----> Add 4.48 to both sides
t = -18.7
