I could be wrong, but I'm pretty sure here the answer would be 10x^2 + 17x +3 would be the area since you have to multiply length and width. since these are expressions with no answers and no other numbers, we can't find x.
9cm
Imagine there are 2 triangles solve for one 3*3=9\2=4.5
Then add
4.5+4.5=9