Let the number of hours = h
You need to multiply the number of hours by the hourly rate for each DJ.
DJ A is 75.30 + 12.50h
DJ B is 52.90 + 18.10h
To find when they will be the same set the two equations to equal each other and solve for h:
75.30 + 12.50h = 52.90 + 18.10h
Subtract 52.90 from each side:
22.40 + 12.50h = 18.10h
Subtract 12.50h from each side:
22.40 = 5.60h
Divide both sides by 5.60:
H = 22.40 / 5.60
H = 4
They will be equal at 4 hours worked.