Question

The other one is for the two variable equation y = 3x + 4 find the matching y value when x = 0

Answer 1

In finding the matching value of one unknown variable when other is known we have to use substitution. By way of substitution, y = 3 (0) + 4; y = 4. Moreover, when the variable of the known variable is zero, we just have to identify the intercept of line in  the equation. The number with no variable in its side is always the intercept of the equation.