Hallo,
(3m+5)(3m-5)+(3m-5)²=2(3m-4)²-4
9 m^2-25 +9 m^2 -30m +25 = 2(9m^2 -24m +16) -4
9 m^2-25 +9 m^2 -30m +25 = 18 m^2 -48m +32) -4
-25 +18 m^2 -30m +25 = 18 m^2 -48m +32 -4 | -18 m^2
-25 -30m +25 = -48m +32 -4
-30m = -48m +28 | +48m
18m=28 | :18
m=14/9