Which answer choice correctly represents an algebraic expression for the sum of 15 and a number? PLS HELP​

Jack did 3/5 of all problems on his weekend homework before sunday. on sunday he solved 1/3 of what was left and the last 4 problems. how many problems were assigned for the weekend?

What is the effect on the graph of the function f(x)=x when f(x) is replaced with -f(x)+4

3x + 4y = 5 x- 3y = -7 solve by substitution