We know that Luke lost x pounds the first week.
We also know that the second week 3/2 less than 3/2 times the pounds he lost the first week, this means that the secons week he lost:
![(3)/(2)x-(3)/(2)](https://img.qammunity.org/2023/formulas/mathematics/high-school/p1ubn0p4hlfpgfknmyepxw1tvkzs8yj6kx.png)
Finally the third week he lost 1 pound more than 3/4 of the pounds he lost the first week. This can be written as:
![(3)/(4)x+1](https://img.qammunity.org/2023/formulas/mathematics/high-school/x96ucmijfs9drqbaglvwjr5nd2qzsrebyr.png)
Hence luke lost a total of:
![x+(3)/(2)x-(3)/(2)+(3)/(4)x+1=(13)/(4)x-(1)/(2)](https://img.qammunity.org/2023/formulas/mathematics/high-school/rhxx8bjlbb0vuuqtdsi1jk24oh2ztifxli.png)
Therefore the expression for Luke's weight loss is:
![(13)/(4)x-(1)/(2)](https://img.qammunity.org/2023/formulas/mathematics/high-school/25vjgrgqf5ebddi4fiqx2aoubh9zla48oj.png)
Liam lost the first week 1 pound less than 3/2 times the loss Luke had the first week this can be express as:
![(3)/(2)x-1](https://img.qammunity.org/2023/formulas/mathematics/high-school/1dyuljhb5g7tu90ipyizexosvbdvgn9rkm.png)
The second week he lost 4 pounds less than 5/2 times the loss of Luke the firs week then we have:
![(5)/(2)x-4](https://img.qammunity.org/2023/formulas/mathematics/high-school/5iq1r3w8q8khghslvjly25uaeaetoopt0d.png)
Finally Liam lost 1/2 pound more than 5/4 times the loss of Luke the first week, then:
![(5)/(4)x+(1)/(2)](https://img.qammunity.org/2023/formulas/mathematics/high-school/vrergm06h4u7kdqe5jeh3r2k0naf22q48x.png)
Adding this we have:
![(3)/(2)x-1+(5)/(2)x-4+(5)/(4)x+(1)/(2)=(21)/(4)x-(9)/(2)](https://img.qammunity.org/2023/formulas/mathematics/high-school/kiezoqw5sl2iwxxnln9tbcvxxed29bwve9.png)
Therefore Liam's expression is:
![(21)/(4)x-(9)/(2)](https://img.qammunity.org/2023/formulas/mathematics/high-school/3kniql42gsdk1og5wl1qqat9y9nr0hwlrw.png)
Now, we know that both of them lost the same weight, then we have the equation:
![(13)/(4)x-(1)/(2)=(21)/(4)x-(9)/(2)](https://img.qammunity.org/2023/formulas/mathematics/high-school/joibx3hpdrfgr0hficucpxbo14oz53gmeu.png)
Solving for x we have:
![\begin{gathered} (13)/(4)x-(1)/(2)=(21)/(4)x-(9)/(2) \\ (21)/(4)x-(13)/(4)x=(9)/(2)-(1)/(2) \\ (8)/(4)x=4 \\ x=(4)/((8)/(4)) \\ x=2 \end{gathered}](https://img.qammunity.org/2023/formulas/mathematics/high-school/a42g3cbyd5a57r2dvjplb1l2lz1s3hy7rk.png)
Therefore Luke lost 2 pound the first week.
Finally we plug the value of x in the expression for Luke's weight loss to get the total amount over the three weeks:
![\begin{gathered} (13)/(4)(2)-(1)/(2)=(13)/(2)-(1)/(2) \\ =(12)/(2) \\ =6 \end{gathered}](https://img.qammunity.org/2023/formulas/mathematics/high-school/icfhum29pi38ffy9hr5kwcihirbgpb4a11.png)
Therefore they lost 6 pounds in three weeks.