Write two equations to model the growth of each tree, and set the equal to each other.
Let x equal the years.
For Type A, the equation is 3x+48 because the tree grows at 3 inches per year and, it started at 4 feet (48 in).
For Type B, the equation is x+72 because the tree grows at 1 inch per year, and it started at 6 feet (72 in).
3x+48=x+72
*Isolate the variable by subtracting x from each side*
2x+48=72
*Subtract 48 from both sides*
2x=24
*Divide both sides by 2*
x=12 years
Hope this helps!!