Step-by-step explanation:
y |X(the sign for protionality) 1/√x
y = 7 when x = 36
y = k/√x
7 = k/√36
7 = k / 6 cross multiply
k = 7×6
k = 42
find y when x is 4
y = 42/√x
y = 42/√4
y = 42/2
y = 21