Final answer:
The expression showing how many sketches each pen pal received is a) 's ÷ 9'. The question involves dividing Mika's total number of sketches by the number of pen pals she has, which is 9.
Step-by-step explanation:
The student is asking how to determine the number of sketches each pen pal received if Mika divided her s sketches evenly among her 9 pen pals. To find out how many sketches each pen pal received, we need to divide the total number of sketches by the number of pen pals.
The correct expression for this division is s ÷ 9. Neither of the multiplication options, s × 9 or 9 × s, would be correct, because they would give us the total number of sketches if each pen pal had received 9 times the amount of sketches Mika originally had. And the division 9 ÷ s would imply we're dividing 9 sketches among s pen pals, which is the opposite of what was asked.
Therefore, the correct choice is a) s ÷ 9, because it correctly represents dividing the total number of sketches s by the number of pen pals, which is 9.