First, add color(red)(7) to each side of the equation to isolate the q term and keep the equation balanced:
3/4q - 7 + color(red)(7) = 8 + color(red)(7)
3/4q - 0 = 15
3/4q = 15
Next, multiply each side of the equation by color(red)(4)/color(blue)(3) to solve for q while keeping the equation balanced:
color(red)(4)/color(blue)(3) xx 3/4q = color(red)(4)/color(blue)(3) xx 15
cancel(color(red)(4))/cancel(color(blue)(3)) xx color(blue)(cancel(color(black)(3)))/color(red)(cancel(color(black)(4)))q = color(red)(4)/color(blue)(3) xx (3 xx 5)
q = color(red)(4)/cancel(color(blue)(3)) xx (color(blue)(cancel(color(black)(3))) xx 5)
q = 4 xx 5
q = 20