Help! Can someone help me answer this/ write it as an equation or something?

Question

Last week Carl bought m pounds of potatoes for his restaurant at a cost of y cents per pound. This week he bought n more pounds than last week at a cost that was z cents per pound greater. What was the difference between the amount he paid for the potatoes last week and the amount he paid this week?

Answer 1

P_{lw= $m*y}

P_{tw = m*y + n(y+z)}

_{Ptw - Plw = (my+ny+nz) - my}

_{= ny+nz = n(y + z)}

_

Answer 2

Last week he bought m pounds of potatoes at y cents a pounds so he paid m*y cents

This week he bough m+ n pounds of potatoes at y+z cents per pound so he paid (m+n)(y+z) cents, which expanded equals m*y + m*z + n*y + n*z

The difference of those two amounts is (m*y + m*z + n*y + n*z) - m*y = m*z + n*y + n*z