Nice systems-of-equations DS question. Let me walk through the structure.
Key concept being tested: Systems of linear equations in Data Sufficiency — specifically, when do you have enough equations to solve for the unknowns you need?
Setup: Total fare = 20 + (passengers − 4)x + (suitcases − 6)s + (km − 5)k, where charges x, s, k only apply when the threshold is exceeded.
Smith family: 14 passengers, 11 suitcases, 20 km
Smith fare = 20 + (14−4)x + (11−6)s + (20−5)k = 20 + 10x + 5s + 15k
Evaluating Statement (1): Jones family — 10 passengers, 9 suitcases, 6 km, fare = $38.
Jones fare = 20 + 6x + 3s + 1k = 38 → 6x + 3s + k = 18
One equation, three unknowns. Insufficient.
Evaluating Statement (2): Baker family — 8 passengers, 8 suitcases, 11 km, fare = $40.
Baker fare = 20 + 4x + 2s + 6k = 40 → 4x + 2s + 6k = 20 → 2x + s + 3k = 10
One equation, three unknowns. Insufficient.
Both together:
From Statement (2): 2x + s + 3k = 10 → multiply by 5: 10x + 5s + 15k = 50
Smith fare = 20 + 50 = $70
The beautiful thing here: you never need to find x, s, and k individually. The combined statement gives you exactly 10x + 5s + 15k — the precise expression in Smith's fare formula — in one step.
Common trap: Students set up three equations hoping to solve for x, s, k separately and panic when they can't (you only have 2 equations from both statements combined). The trick is to check whether Statements 1 and 2 together produce the exact linear combination you need for Smith, even without isolating each variable.
Answer: C (Both statements together are sufficient.)
Takeaway: In DS with multiple unknowns, always check if the combined statements produce the exact expression the question needs — individual variable values aren't always required.