Solve each equation and verify the solution

First one (thers are similar)

5 + 2x = 25     subtract 5 from both sides of the equation to get

2x = 20            now divide both sides by to to get

x = 10 

CHECK:    5 + 2(10) = 25

                  5 + 20 = 25

                       25   = 25     !   Verified !  

You can do the others....

for simultanous equations. I found https://www.equationcalc.com/simultaneous-equation-solver  useful