1) 13a=-5
Make a the subject of the formula by dividing both sides by 13(the coefficient of a)
13a/13=-5/13
Therefore a= -0.385
The second one). 12-b= 12.5
You take the 12 to the other side making b subject of the formula (-b in this case)
-b= 12.5-12
-b= 0.5
(You cannot leave b with a negative sign so you will divide both sides by -1 to cancel out the negative sign)
-b/-1= 0.5/-1
Therefore b=-0.5
The third one). -0.1= -10c
You will divide both sides by the coefficient of c(number next to c) which is -10
-0.1/-10= -10c/-10
Hence, c= 0.01