The smaller triangle was dilated to form the larger triangle. What is the value of x?

7.5

scale factor=measure larger triangle/measure smaller triangle>18/12

scale factor=1.5

so

measure larger triangle=scale factor*measure smaller triangle

for the leg in the smaller triangle equal to 5

measure larger triangle=1.5*5> 7.5

the answer is

7.5

Explanation:

coil wire, increase current, put iron inside the coil