The temperature is -4°f. a high pressure front increases the temperature to 8°f. by how many degrees did the temperature increases?

The temperature had to rise 4 degrees to reach zero, and then another 8 degrees to reach 8.  The total increase was (4 + 8) = 12 degrees.

A more formal way to do it:

The change is (end value) minus (start value)

Change = (8) - (-4) = (8) + (4) = 12 degrees.

plants store their excess carbohydrate in the form of starch so that it could be used as energy source later on. the excess carbohydrate is converted into starch in the plastid i.e. chloroplast & this process occurs in the presence of sunlight. it is an insoluble polymer of glucose which gets stored in cell organelles named as amyloplasts. in some plants, starch is also stored in roots and embryos.