If you mean to write it as an inequality, then: 3/4x - 9 ≥ 42
3/4 of a number refers to three quarters of some variable, represented by "x". Decreased by nine indicates you're subtracting the term by 9. "At least" means greater than or equal to - you don't want it "at most"; that limits it to 42 and below. "At least" also indicates that you want to include the value 42 since 42 is at least 42.
