To solve the equation 3x + 7x = 12, we first combine the like terms on the left side. The terms 3x and 7x can be added together:
3x + 7x = 10x
This simplifies our equation to:
10x = 12
Next, to find the value of x, we need to isolate x. We do this by dividing both sides of the equation by 10:
x = 12 / 10
This simplifies to:
x = 1.2
So, the value of x when 3x + 7x = 12 is 1.2.