well this is smthing related to math ..... but here's how we do it :
3x = -15 .... 3x is in multiplication form ..... and when it comes to the right it changes to division form.....which will become
x = -15/3 and if we divide 3 and 15 we get 5 as 3 × 5 = 15
and as (+) and (-) = (-) ... the answer will be negative ... so the answer is -5
