Answer 1

B = {P : P ∈ W and p² < 20}
When p² = 0
P = `sqrt(0)` = 0

When p² = 1
P = `sqrt(1)` = 1

When p² = 4
P = `sqrt(4)` = 2

When p² = 9
P = `sqrt(9)` = 3

When p² = 16
P = `sqrt(16)` = 4

∴ Roster form of the given set B = {0, 1, 2, 3, 4}