Specific heat 4.28J(g*C)
Density 1.02g/ml
30ml of solution A
40ml of solution B
Change in temperature 3.9 degrees C

Use Q = mcT

Q is what you are looking for.
m is the total mass of solution.
c is the specific heat capacity.
T is the change in temperature (Final temperature - Initial temeprature)

What do you get as answer?