11x+3y=103 and y=3x+1.
11x+3(3x+1)=103 -----> plug in (3x+1) for y in the first equation. You will want to distribute the 3 to the 3x+1 to get something that looks like:
11x+9x+3=103 ------> now you want to combine like terms
20x+3=103 ---> subtract 3 from both sides
20x=100 ----> divide both sides by 20
x=5
y=3(5)+1 ---> I like to plug in this to the equation that already has y isolated. 3*5 is 15, add 1 and you find that y=16.
(5, 16) will be your final answer (: