4. Find the area of a triangle two sides of which are 18 cm and 10 cm and the perimeter is
42 cm.

Let the sides of a triangle a = 18 cm, b = 10 cm and c

We have, perimeter = 42 cm

So, a + b + c = 42

By substituting the values,

18 + 10 + c = 42

28 + c = 42cm

c = 42 - 28 cm

Thus, c = 14cm

Now, we know that,

Therefore,

Now, Area of triangle =

=

=

=