Since we know that CE and FH are congruent, then DP and PG are also congruent. So, we can solve this problem by setting the two given expressions equal to each other and finding the value of x.
6x - 3 = 3x + 6
3x - 3 = 6
3x = 9
x = 3
PG = 3x + 6
PG = 3(3) + 6 = 15 units
Hope this helps!! :)