Question 319797
Use Heron's Formula to find your area. The triangle has 3 different sides and so this tells me that it is a scalene triangle.

Let sqrt = square root

Let A = area of scalene triangle

Let a + b + c = sides of triangle

Let s = half of the triangle's perimeter

s = (a + b + c)/2

The formula is A = sqrt{s(s - a)(s - b)(s - c)}

The given sides: 

a = 20
b = 31
c = 43

We need to find the value of letter s as step one.  Just plug and chug.

s = (20 + 31 + 43)/2

s = 94/2

s = 47

We can now use the formula given above.

A = sqrt{s(s - a)(s - b)(s - c)}

We also plug and chug.

A = sqrt{47(47 - 20)(47 - 31)(47 - 43)}

A = sqrt{47(27)(16)(4)}

A = sqrt{47(1728)}

A = sqrt{81216}

A = 284.9842101, Which can be rounded to the nearest unit (or ones place) to make the answer 285.

To learn more about Heron's Formula, copy and paste the link below.

http://www.mathsisfun.com/geometry/herons-formula.html