I could see why your teacher would ask you this, as both sonnets talk about love and time and the idea of lasting forever. But the sonnets are actually quite different if you look closely. Let's start with Sonnet 18, perhaps the most famous of the sonnets. As the poet compares his love's (a boy? a girl? himself?) beauty to things in nature, nature can't stack up. Summer is too short, the sun too hot. And nature's beauty fades, as does a person's as they age. But not his love's; his love's beauty is eternal, and Death will not brag about having taken the object of the poem because he or she is just that: the object of the poem. "When in eternal lines to time thou growest" means that the person who the poem is about will live forever because their beauty will forever be captured by the poetry. Many of the surrounding sonnets to 18 are also about this same theme - poet as eternally and infinitely powerful. The poet has the power to make whatever he wants last forever. But then we get to 116, and the poet's confidence seems to have dipped slightly. Here is actually is talking about love, and love is now in the driver's seat, not the poet. Love is permanent here, an "ever fixed mark," that is not "Time's fool." The power has been taken away from the poet in this sonnet and put squarely in the hands of lvoe. In fact, you get the sense that the poet is so smitten with someone that he feels powerless to stop his emotions. So in love, and so sure of love's capacity, that he is willing to bet his occupation on it - if what he has proclaimed about love is not true, he has never written anything. Quite the opposite sentiment from 18. All you have to do is look closely.