The scale drawing's measurements will be 1 inch by 0.8 inch.
The scale is 1 in: 10 feet; because the deck's real width is 10 ft, the scale can read 1 inch. To evaluate the width: 1/10 = x/8
Cross multiply:
1*8 = 10*x
8 = 10x
Divide both sides by 10:
8/10 = 10x/10
0.8 = x
The scale drawing's width would be 0.8 inches.