Question

12-11a=45

Answer 1

subtract 12 and divide by -11.
12-11a=45
-12 -12
-11a/-11 =33/-11
a=-3

Answer 2

this is the general process
isolate the term(s) with the variable(s) to one side
simplify if possible by adding like terms
divide by the coefficient of the variable so it becomes 1*variable
remember whatever you do to one side of the equation also do to the other to maintain the value (balance)
if you ever have a fraction start by multiplying each term by the lowest common multiple to get rid of the fraction

Answer 3

12-11a=45