Connie can clean her house in 2 hours so Connie can clean 1/2 of the house per 1 hour.

Together Connie and Alvaro can clean the house in 1hr 15 min = 1 + 15/60 = 1 + 1/4 = 5/4 therefore the can clean 1/(5/4) = 4/5 of the house per hour.

Let 'x' be the hours that Alvaro needs to clean the whole house by himself then he can clean 1/x of the house per hour.

Thus we have, in 1 hour time together they will clean

1/2 + 1/x = 4/5 multiply both sides by 10*x

5*x + 10 = 8*x

x = 10/3 hours = 3 1/3 hr = 3 hr 60/3 min = 3 hr 20 min

Alvaro needs 3 hr 20 min to clean the house by himself.