Your mixture contained sand, salt, and something else (#"X"#?).
Your data are:
a) dish = 21.45 g
b) dish + sand + salt + #"X"# = 33.62 g
c) dish + sand + salt = 27.83 g
d) dish + sand = 25.46 g
Mass of sand = (dish + sand) – (dish) = 25.46 g – 21.45 g = 4.01 g
Mass of salt = (dish + sand + salt) – (dish + sand) = 27.83g – 25.46 g = 2.37 g
Mass of X = (dish + sand + salt + #"X"#) –(dish + sand + salt) = 33.62 g – 27.83 g = 5.79 g
Mass of mixture = (dish + sand + salt + #"X"#) – (dish) = 33.62 g – 21.45 g = 12.17 g
#"% of a component" = "mass of component"/"mass of mixture" × 100 %#
#"% Sand" = "mass of sand"/"mass of mixture" × 100 % = (4.01 color(red)(cancel(color(black)("g"))))/(12.17 color(red)(cancel(color(black)("g")))) × 100 % = 32.9 %#
#"% Salt" = "mass of salt"/"mass of mixture" × 100 % = (2.37 color(red)(cancel(color(black)("g"))))/(12.17color(red)(cancel(color(black)("g")))) × 100 % = 19.5 %#
#"% X" = "mass of X"/"mass of mixture" × 100 % = (5.79 color(red)(cancel(color(black)("g"))))/(12.17 color(red)(cancel(color(black)("g")))) × 100 % = 47.6%#