Answer:
3x-21+4=28-2x...... Multiply 3 with (x-7)
3x+2x=28+21-4......Take - 2x from right side to left side which makes it +2x and - 21+4 from left side to right side which makes it +21-4
5x=45.....Add and subtract as required
x=45/5....Taking 5 from left side to right side and dividing it
x=9.....Normal division