Let's take this step-by-step.

**Step 1. Convert 1 ft to centimetres**

#1 color(red)(cancel(color(black)("ft"))) × (12 color(red)(cancel(color(black)("in"))))/(1 color(red)(cancel(color(black)("ft")))) × "2.54 cm"/(1 color(red)(cancel(color(black)("in")))) = "30.5 cm"#

**Step 2. Convert #"1 ft"^3# to cubic centimetres**

#1 color(red)(cancel(color(black)("ft"^3))) × (("30.5 cm")/(1 color(red)(cancel(color(black)("ft")))))^3 = "28 300 cm"^3#

**Step 3. Calculate the mass of the silver**

#"Mass of Ag" = "28 300" color(red)(cancel(color(black)("cm"^3color(white)(l) "Ag"))) × "10.5 g Ag"/(1 color(red)(cancel(color(black)("cm"^3color(white)(l)"Ag")))) = "297 000 g Ag"#

**Step 4. Convert the mass of silver to kilograms**

#"Mass of Ag" = "297 000" color(red)(cancel(color(black)("g Ag"))) × "1 kg Ag"/(1000 color(red)(cancel(color(black)("g Ag")))) = "297 kg Ag"#