Without a vale to substitute for the variable, we can only simplify the expression: since [tex] 8=4\cdot 2 [/tex] and [tex] 50 = 25\cdot 2 [/tex], the expression becomes
[tex] -4\sqrt{8m} + 7\sqrt{50m} = -4\sqrt{2\cdot 4m} + 7\sqrt{2\cdot 25m} [/tex]
Now use the property [tex] \sqrt{ab} = \sqrt{a}\sqrt{b}\ \forall\ a,b\geq 0 [/tex]
[tex] -4\sqrt{4}\sqrt{2m} + 7\sqrt{25}\sqrt{2m} = -8\sqrt{2m}+35\sqrt{2m} [/tex]
Now we can factor [tex]\sqrt{2m}[/tex]:
[tex] -8\sqrt{2m}+35\sqrt{2m} =\sqrt{2m}(-8+35) = 27\sqrt{2m}[/tex]
