Express x/4-3+x/7 in single fraction

Answer 1

using a common denominator of 28,
x/4 - 3 + x/7 = 7x/28 - 84/28 + 4x/28 = (11x-84)/28
But maybe you meant
x/4 - (3+x)/7 = (7x - 4(3+x))/28 = (3x-12)/28