To which set of numbers does the number -12 belong?

That belongs to the integers set, also rational and real number set

integers are like -4,-3,-2,-1,0,1,2,3,4 etc
rational numbers are number that can be written in form a/b where a and b are integers and b≠0
real numbes include rational numbers

so integers, rational number and real numbers

He was paid 23 dollars for each lawn

If you make it a little more clear i can answer it