Please help, I missed class and I don't know how to solve these types of equations. An answer with the steps/explanation would be helpful :)

Tomas used 3 1/3 cups of flour and now has 1 2/3cups left. which equation can he use to find f, the number of cups of flour he had to begin with? f+3 1/3=1 2/3 f-3 1/3=1 2/3 3 1/3f=1 2/3 f/3 1/3=1 2/3

Atriangular field has sides of lengths 21, 39, and 41 yd. find the largest angle. (round your answer to the nearest degree.)

Is triangle jkl congruent to triangle rst? if so, what is the scale factor?