What frequency range is occupied by a 3 kHz LSB signal when the displayed carrier frequency is set to 7.178 MHz?
Why On lower sideband the transmitted energy sits entirely below the suppressed carrier frequency shown on the display. A 3 kHz wide signal therefore extends from 7.178 MHz minus 3 kHz up to the displayed frequency, so it occupies 7.175 to 7.178 MHz. This matters near band edges: on LSB you must stay at least 3 kHz above the lower edge, and on USB at least 3 kHz below the upper edge.
Watch out The range running up to 7.181 MHz is what a USB signal on the same dial reading would occupy, since upper sideband puts the energy above the carrier frequency.
LSB goes down, USB goes up. Subtract or add 3 kHz to the dial reading.