z or t Argggggggg

Among trained typists, suppose the average typing speed on an electric typewriter is 60 words per minute (wpm), with a standard deviation of 5 wpm. The manufacturer of a personal computer claims that their PC will improve typing speed. A random sample of 90 typists is tested on the PC and the mean wpm is 65. Test the hypothesis that using this PC affects typing speed. Set Alpha at 0.05.
a. Should you use the z distribution or t distribution? Why?
Level of measurement is interval/ordinal
b. State H0 and H1.
Ho no difference H1 difference
c. What is the critical value?
one or two tail unsure
d. What is the obtained statistic?
e. Should you reject the null hypothesis?

f. Is there sufficient evidence to support the manufacturer’s claim?

Ok my reakonings
Level of measurement is interval/ordinal and
Critical value depends on one or two tail 1.64 or 1.
a) we have the std dev for pop and sample is 90 Z test??
b)Ho would say that the PC doesnt effect
H1 the Pc does effect
c)Believe this is a single tail 1.96Z??
d)z=65-60 / 5/root of 90??
= 9.49 dont know what this means
e) Yes???
f) yes