First find the perimeter of the rectangle
P = 2(l+w) where l is the length and w is the width
P = 2( 5x-1+x)
Combine like terms
P = 2( 6x-1)
P = 12x -2
Find the perimeter of the triangle
P = s1 + s2 +s3 where s is the side length
P = 5x+12+ 6x+7
Combine like terms
P = 11x+19
We are told the perimeters are equal
12x-2 = 11x+19
Subtract 11x from each side
12x-2 -11x = 11x+19-11x
x-2 = 19
Add 2 to each side
x-2+2 = 19+2
x = 21
The side lengths of the rectangle are
x=21 and 5x-1 = 5*21 -1 = 105-1 = 104
We can find the area
A = l*w where l is the length and w is the width
A = 21 * 104
A = 2184 units^2
Answer:
B 2184 units^2