Finding proportions of populations and probability from normal distribution?

"A consumer survey indicates that the average household spends mean= 155 on food each week. The distribution of spending amounts is approximately normal with a standard deviation of σ= $25.

a. What proportion of the population spends more than $175 a week on groceries?

b. What is the probability of randomly selecting a family that spends less than $100 on groceries?

c. How much money do you need to spend on groceries to be in the top 20% of the distribution?"

I'm at a loss for how to solve this. Do I need to make a bell curve, or can I just use straight math to solve it? Do I need a z-table?