12. In one morning,if the shadow of a building of 15 meters long is 12 meters, then how long is the shadow of a tree of 35 meters long in meters? A) 28 C. 30 B. 20 D. 17 13. What is the slzo of the matrix (} 2&-1&4 9&5&-3 ) C. 2times 2 2times 3 B. 3times 2 D. 3times 3

12. To solve this problem, we can use the concept of proportionality. The length of the shadow of an object is proportional to the height of the object. In this case, the height of the building is 15 meters and its shadow is 12 meters. We need to find the length of the shadow of a tree that is 35 meters long.

Let's denote the length of the shadow of the tree as x. We can set up a proportion:

$\frac{{\text{{length of the shadow of the building}}}}{{\text{{height of the building}}}} = \frac{{\text{{length of the shadow of the tree}}}}{{\text{{height of the tree}}}}$

Substituting the given values, we have:

$\frac{{12}}{{15}} = \frac{x}{{35}}$

To solve for x, we can cross-multiply:

$12 \times 35 = 15 \times x$

$420 = 15x$

Dividing both sides by 15, we get:

$x = \frac{{420}}{{15}}$

$x = 28$

Therefore, the length of the shadow of the tree is 28 meters. The correct answer is A) 28.

13. The size of a matrix is determined by the number of rows and columns it has. In the given matrix, there are 2 rows and 3 columns. Therefore, the size of the matrix is $2 \times 3$. The correct answer is B. $2 \times 3$.