Two Population Means with Known Standard Deviations · Exercise 12

Two metal alloys are being considered as material for ball bearings. The mean melting point of the two alloys is to be compared. 15 pieces of each metal are being tested. Both populations have normal distributions. The following table is the result. It is believed that Alloy Zeta has a different melting point.
$$\begin{array}{ccc}& \text{Sample Mean Melting Temperatures (°F)}& \text{Population Standard Deviation}\\ \text{Alloy Gamma}& \text{800}& \text{95}\\ \text{Alloy Zeta}& \text{900}& \text{105}\end{array}$$

Is this a right-, left-, or two-tailed test?

Its source prints no answer for this problem, so there's nothing to check against.

OpenStax, Introductory Statistics 2e · §10.2 Two Population Means with Known Standard Deviations · Exercise 12