t-12<-4, add 12 to each side of the inequality:
t<8.
To represent this graphically, use a number line. Mark 8 on the number line.
The part of the line to the left of 8 represents t<8, so shade this part of the line (without including 8 itself). t<8 is everything to the left of 8, but you can only show part of this on the graph. Indicate (perhaps by using an arrow) that the line continues indefinitely to the left.
If you draw a tiny circle at the point 8 this represents the fact that 8 itself is not included in the inequality.