7x = 105 what is the value of x?

Aclassmate thinks that solving a system by graphing gives an exact answer when the lines appear to cross at a grid point, but only an approximate answer when they don't. explain why this isn't true.

Solve the inequaliy: (x^2+2)(x−2)^2(6−2x)> 0

Find the percent error of the measurement 4 cm