Answer: 7 ounces
Explanation:
Let x = Weight of one blue block.
y = Weight of one red block.
As per given , we have the following system of equation:

Multiply 4 to equation (2) , we get

Eliminate (1) from (3) , we get

i.e. Weight of one red block = 4 ounces
Put value of y in (2) , we get

i.e. Weight of one blue block = 3 ounces
The combined weight of one red block and one blue block = 4+3 = 7 ounces