A(x) = 12.85x + 53 where x is the number of hours that Maria worked in a week
B(x) = 7.55x + 143 where x is the number of hours that Sara worked in a week
we will change the "x" by "y" on the Sara's equation to make a difference with Maria's
So the equation for Sara would be:
B(y) = 7.55y + 143
If the add their earnings, that means we have to add A(x) and B(y)
Total earnings = A(x) + B(y) = (12.85x + 53) + (7.55y + 143)
Total earnings = 12.85x + 7.55y + 53 + 143
Total earnings = 12.85x + 7.55y + 196
So the answer is: 12.85x + 7.55y + 196
where x is the number of hours that Maria worked in a week
and y is the number of hours that Sara worked in a week