Answer:
The rectangle's area is 48 square meters
Explanation:
Recall that the perimeter of a rectangle of base b and height h is given by the formula:
Perimeter = 2 b + 2 h
we know that the perimeter is 28 meters, then we can create our first equation;
2 b + 2 h = 28
which means:
2 (b + h) = 28
b + h = 28/2
b + h = 14
the tell us that the diagonal is 10 meters, so we use the Pythagorean theorem to write a second equation using the rectangle's base, height, and diagonal (which form in between the three a right angle triangle where the hypotenuse is the rectangle's diagonal:

So, we can use the equation : b + h = 14 to write one variable in terms of the other one and use it as substitution in the second (quadratic) equation:
h = 14 - b
then:

which we have reduced at the end by dividing both sides by 2.
we can use factoring to solve these equation;

Se we find two possible solutions: b = 6 m or b = 8 m
If we call b = 8 m, then the height becomes h = 14 - (8) = 6 m
and viceversa.
So a rectangle with such dimensions will render an area that equals :
Area = b x h = 8 x 6 = 48 square meters.