Distribute the 3 to both t and -7
3(t) = 3t
3(-7) = -21
3t -21 = 6t
isolate the -21 by subtracting 3t from both sides
-21 + 3t = 6t
-21 + 3t (-3t) = 6t (-3t)
-21 = 3t
divide 3 from both sides to isolate the t
3t = -21
3t/3 = -21/3
t = -21/3
t = -7
t = -7 is your answer
hope this helps