Let C = cost of yacht and x= equal cost of each person
Three people decided to share the cost of yacht means
x+x+x=C
3x=C
x=C/3----> eq.1
By bringing in an additional partner, they can reduce the cost to each person by $4000 means
“C/4 = x - $4000”---> eq.2
Substitute eq. 1 in eq. 2 then Solve:
C/4 = x - $4000
C/4 = (C/3) - $4000
C/3-C/4 = $4000---> find LCM of 3 and 4
4C - 3C/12=$4000
C/12=$4000
C=$4000 * 12
C=$48000---->answer
The total cost of yacht is $48000