Consider the rectangle drawn below,
Consider the properties of rectangle that the opposite sides are equal, and both the diagonals are also equal in length.
[tex]QS=RT\Rightarrow3x+7=5x-3\Rightarrow5x-3x=7+3\Rightarrow2x=10\Rightarrow x=5[/tex]Thus, the value of 'x' is 5.
Substitute the value to obtain the diagonal QS as,
[tex]QS=3(5)+7=15+7=22[/tex]Similarly solve for the diagonal RT as,
[tex]RT=5(5)-3=25-3=22[/tex]Already we knew that the diagonal will be equal with the length 22 units.