Since David has to buy the avocadoes, we can multiply 3 by $1.50, which gives us $4.50 and will be a constant in the equation
Only the number of pounds of apples can vary (we will name the variable 'p')
Since he can spend LESS than 15, we have to use the sign <
If we combine it all together we get:
4.50+1.00p<15
4.5+p<15