**Concept: The question is based on the application of Triangle area**

**Solution:**

Consider the triangle with the side of 12 units as base & height 3 units,

=>Area = ½ *12*3 unit square (1)

Consider the triangle with the side of 7 units as base & height as x units,

=>Area = ½* 7*x unit square (2)

From 1 & 2

½* 12*3 = ½* 7 * x (As we are calculating the area of the same triangle)

=>x = 36/7

**option(c)**