so lets write this equation out. Let x be that number we are trying to find.
So five-sevenths is a fraction that is written like this
5/7
when you see the word "of" that means multiplication
so we can write the full equation.
(5/7)x = -35
now we can solve
Multiply both sides by 7
5x = -245
now divide by 5
and we get
x = -49