Answer:
see below
Explanation:
Filling the given numbers into the given formulas, you have ...
Line AB:
x = 1 +(4-1)t, y = 1 +(3-1)t
x = 1+3t, y = 1+2t . . . . . . simplify
Line BC:
x = 4 +(1-4)t, y = 3 +(7-3)t
x = 4 -3t, y = 3 +4t . . . . . simplify
Line AC:
x = 1 +(1-1)t, y = 1 +(7-1)t
x = 1, y = 1+6t . . . . . . . . . .simplify