Answer: Jim can lay 25 tiles per hour.
Explanation:
 Let be "x" Jim's rate and "y" Pete's rate.
 We know that Jim completed half the floor in 4 hours, then:
 

 And Pete completed the other half of the floor in 2 hours, then:
 

 Since Jim completed half the floor and Pete completed the other half:
 
 [Equation 1]
 We also know that Pete can lay 25 more tiles per hour than Jim, then:
 
 [Equation 2]
 Then, we can substitute Equation 2 into Equation 1 and solve for "x":
 

 Therefore, Jim can lay 25 tiles per hour.