A) 9 1/3
1) We can find that unit rate by setting a proportion. But before that, we need to convert those Mixed Numbers into improper fractions:
km hours
21/2 -------- 9/8
x-------------------- 1
21/2x = 9/8
2)
Cross multiplying it we have 28/3 as an improper fraction, and that rewritten as Mixed Number is equal to 9 1/3
3) Hence, Xavier makes 9 1/3 km per hour A) 9 1/3