Cross Multiplication!
[tex] \frac{4}{7} [/tex] = [tex] \frac{x-3}{21} [/tex]
4 × 21 = 7 × (x-3)
Distribute 7 into the parenthesis:
84 = 7x - 21
Take 21 to the other side:
84 + 21 = 7x
105 = 7x
Divide by 7 on both sides:
[tex] \frac{105}{7} [/tex] = [tex] \frac{7x}{7} [/tex]
( 7 and 7 cancels out )
15 = x
x = 15
