y = A sinX
Maximum value= 15
Minimum value= 9.4
Amplitude= ( 15 - 9.4 )= 5.6/2 hours
Vertical shift = 15 - 2.8= 12.2 hours
Phase shift
June = 6th month
December= 12th month
X + delta
when x= 15 , sin ( 6 /12+ delta) = 1
and. x = 9.4 ,. Sin (12/12 + delta) + 2.8 = 0
then
Sin ( 6 /12 + delta) = 1
arcsin 1= 90°
Sin (12/12 + delta) = 2.8/12= 0.23
Then arcsin 0.23= 13.29 °
Then answer is
y = 15• Sin ( X + 0.5)