How do you solve y= 4x + 45 and x= 4y? Algebra Systems of Equations and Inequalities Systems Using Substitution 1 Answer KillerBunny Oct 4, 2015 #x=-12#, #y=-3# Explanation: Knowing that #x=4y#, you can write the first equation as #y=4(4y)+45 -> y=16y+45 -> -15y=45#, isolating the #y#-terms by bringing them all to the left. Now, solving by #y#, we have #y=-3#. Since #x# was #4y#, we know that #x=4*(-3)#, and thus #x=-12# and the system is solved. Answer link Related questions How do you solve systems of equations using the substitution method? How do you check your solutions to a systems of equations using the substitution method? When is the substitution method easier to use? How do you know if a solution is "no solution" or "infinite" when using the substitution method? How do you solve #y=-6x-3# and #y=3# using the substitution method? How do you solve #12y-3x=-1# and #x-4y=1# using the substitution method? Which method do you use to solve the system of equations #y=1/4x-14# and #y=19/8x+7#? What are the 2 numbers if the sum is 70 and they differ by 11? How do you solve #x+y=5# and #3x+y=15# using the substitution method? What is the point of intersection of the lines #x+2y=4# and #-x-3y=-7#? See all questions in Systems Using Substitution Impact of this question 5792 views around the world You can reuse this answer Creative Commons License