Hello!
In rectangles we know that to find perimeter we use: length + length + width + width = perimeter. This can be simplified to 2(length) + 2(width) = perimeter.
We are given equations for length and width and given an amount for perimeter so let's plug it in and solve!
Length = 3x
Width = 4x+3
2(3x) + 2(4x+3) = 146
6x + 8x + 6 = 146
14x = 140
x = 10
Now that we know x, plug it into your length and width equations.
Length: 3(10) = 30
Width: 4(10) + 3 = 43
Length is 30 units and width is 43 units.
I hope this helped! :)