Points D and E are midpoints of the sides of triangle ABC. The perimeter of the triangle is 48 units. Triangle A B C is shown. Point D is the midpoint of side A B and point E is the midpoint of side B C. The lengths of A D and D B are 3 t, the lengths of B E and E C are 4 t, and the length of A C is 7 t + 6. What is the value of t