For the first hour of work, Manolo can make face-masks at the rate of one every four minutes. Thereafter, he can make face-masks at the rate of one every six minutes. How many face-masks does Manola make in a four-hour shift?
He makes 60/4=
<gadget id="calculator">60/4</gadget>
<output>15</output>
15 in the first hour.
He makes 60/6=
<gadget id="calculator">60/6</gadget>
<output>10</output>
10 in each subsequent hour.
There are 4-1=
<gadget id="calculator">4-1</gadget>
<output>3</output>
3 more hours in his shift.
He makes 15+10*3=
<gadget id="calculator">15+10*3</gadget>
<output>45</output>
45.

<result>45</result>