+981 Hi QS!
Since the two shapes are similar, we can set up the following relationship:
Assumption 1: triangle ABE is similar to ACE, CD and BE is parallel
\(\frac{15}{15+3}=\frac{10}{10+x}\\ 15(10+x)=10\cdot{18}\\ 150+15x=180\\ 15x=30\\ x=2\)
Assumption 2: triangle ABE is similar to ACE, CD and BE are not paralle
\(\frac{10}{15+3}=\frac{15}{10+x}\\ 10(10+x)=15\cdot18\\ 100+10x=270\\ 10x=170\\ x=17\)
I hope this helped,
Gavin
