I'm not sure how to do this someoneso much in advance : )

Use 45-45-90 triangle to find the hypotenuse of the dotted triangle which is one of the sides of the shaded one. Use 30-60-90 triangle to find the hypotenuse of the large triangle including the dotted and shaded one. You now have 2 sides down. To find bottom length, find base length of big triangle still using 30-60-90 triangle and find base length of small dotted triangle using 45-45-90 subtract small from big. add together sides and u have it