Question 1021374
Inside surface area for walls is perimeter times height.
Add surface are of floor and ceiling for total surface area:
L=10m; W=8m; H=3m 
.
P=2(L+W)
P=2(10m+8m)
P=2(18m)
P=36m
.
P x H = 36m x 3m=108m^2
.
Surface area of walls is 108m^2
.
Surface area of floor=L x W = 10m x 8m = 80m^2
Surface area of ceiling=L x W=10m x 8m = 80m^2  
.
Total surface area = wall area + floor area + ceiling area
Total surface area = 108m^2 + 80m^2 + 80m^2
Total surface area = 268m^2
.
ANSWER: Total interior surface area is 268 square meters.
.