In these type of questions, we have to substitute the numbers given into the algebraic expression.
when 3x + ky = -1, and x=3 and y=5, we can write this equation to solve for k: 3(3) + k(5) = -1
to solve this, first simplify the numbers. 9 + 5k = -1 shift +9 to the other side and turn it into -9 5k = -1 -9 5k = -10 shift x5 to the other side and turn it to ÷5 k = -10 ÷ 5 k = -2