Which word in Group B can be added to Group A? Why?

Group A: complex, on, rat, stall
Group B: accord, gallop, new, tandem

Letter Equations are well known phrases or facts where the key words have been replaced with the first letter of that word. These are often in the form of an equation, which contain a number, an = sign and the rest of the obscured phrase or fact.

10 = M per P in C C

What does this rebus represent?

2:53 AM = maelstrom
9:48 AM = conundrum
6:17 PM = talisman

Each word in Group A can be paired with a unique word in Group B. What are the pairings? Why?

Group A:
apropos, doughy, gingham, mica, rebuff, scarab, squall, ukulele

Group B:
aloft, amateur, bituminous, enables, melody, phantasm, steroid, summary

Jane wants to make some toast for her breakfast. Unfortunately, her toaster is broken. Can you turn bread into toast by changing one letter at a time? Each step must create a valid word in the English language. Jane made the change in 7 steps. Can you do as well ... or better?

BREAD ---- TOAST

Private Peter Perkins wants to change his branch of military service. He is currently in the army, but wants to join the navy. To leave the army, he must get out of his tank. He then has to go on board a ship to join the navy. Change ARMY to NAVY by changing one letter at a time. The change must go through TANK and SHIP. Each change must produce a valid word in the English language. No word can be used more than once.

ARMY ---- TANK ---- SHIP...