Because it is an equilateral triangle, all three sides are the same length. Because of this, you need to divide 63/3 to find out the length of one side. 63/3=21. So this tells us that 4x+3=21. Now that we have the equation, we need to solve for x. To do this, subtract the 3 on both sides to get 4x alone. 21-3=18. So now we know that 4x=18. Now divide 4 on each side to get x alone. X= 18/4, which simplifies to 9/2. In decimal form, x=4.5.
