Money puzzles

Pick one unknown and call it $x$. Every sentence in the puzzle then becomes an equation involving $x$ (or several unknowns $x,y,\dots$). Before writing anything, change all money to the smallest unit mentioned—pence is usually safest—so a crown is 60 pence, a shilling is 12 pence, and a pound is 240 pence. Do not mix pounds, shillings, and pence in the same equation. Once the equation is built, solve it by ordinary algebra, then check that the answer fits the story: stamp counts must be whole numbers, and no one can have negative money. If several conditions are given, write one equation for each and solve them together. That is the whole method: name the unknowns, unify the units, translate words into equations, solve, and sense-check.