Try this option (not for all the tasks!):
1) rule for n-angle is: S=180°(n-2), where n - number of the sides. S₁₅=180*13=2340°;
2) S₂₅=180*23=4140°;
4) this is deltoid;
5) this is paralelogram;
6) x=130°; y=50°;
10) x=90°; y=30° (it is deltoid);
12) not enough info for parallelogram (the same for deltoid);
14) it is enough: according to a property of a parallelogram (it means that a square and rombus are parallelograms);
15) it is enough according to the properties of parallelograms;
16) x=2; y=1;
18) poit S(0;0); point T(b+c;d). The coordinates of the midpoint are (0.5b+0.5c;0.5d); slope=arctg(d/(b+c)).