Is y-12=19 a solution?

No, this is an equation which you are to solve.

Add 12 to both sides of the equation: y = 19+12, or y = 31 (solution).

no this isnt a solution ... its an equation

an equation is smthing which has variables constants "=" sign and operations

and here ... we need to find the no. of the variable

well ... if u want the solution of this equation here it is:

y - 12 = 19

y = 19 + 12

∴y = 31