Concept:The value of y is given by a linear equation in x. Substitute y=5 into the equation and solve for x.Explanation:The given equation is:y=21x+1Substitute y=5:5=21x+1Subtract 1 from both sides:5−1=21x4=21xMultiply both sides by 2:x=4×2x=8Answer:x=8, which is option A.