A graph of pressure against time shows 6 complete waves in 0.018 s…

Step 1. (a) $T = \dfrac{0.018\ \text{s}}{6} = 0.003\ \text{s}$.

Step 2. (b) $f = \dfrac{1}{0.003\ \text{s}} = 333.3\ \text{Hz}$.

Step 3. (c) The waves get taller (a bigger amplitude); the number of waves in $0.018\ \text{s}$ stays $6$ (the same frequency).