10/(z+3) = 100/(5z-7)

Question

10/(z+3) = 100/(5z-7)

Answer 1

10*(5z-7)/z+3-100*(z+3)/(z+3)(5z-7)=0
50z-70-100z-300/(z+3)(5z-7)=0
-50z-370/(z+3)(5z-7)=0
-50z-370=0
-50z=370
z=370:(-50)
z=-7.4

Comments

А почему z+3 -100×(z+3) и тд.?