m = mass of granite boulder = 20 g
c = specific heat of granite boulder = 0.79 J/gC
T₀ = initial temperature of granite boulder = 10 °C
T = final temperature of granite boulder = 29 °C
Q = heat gained by granite boulder as energy from the sun
heat gained by granite boulder is given as
Q = m c (T - T₀)
inserting the values
Q = (20) (0.79) (29 - 10)
Q = 300.2 J