Just relax, breathe deeply from the diaphragm, allow the
cleansing air to fill your brain, and take it one step at a time.
You said that 3t - 7 = 5t
OK. Fine.
Let's just find out what 6t is.
Subtract 3t from each side: -7 = 2t
Multiply each side by 3 : -21 = 6t
Did I go too fast for you ?