This one was fairly easy as it looks very much like leaf scorch and is caused by the plant drying out too much in hot weather, or sometimes by too strong a fertiliser. Just keep the soil moist and try to spray the plants with water a few times a day if is really hot or even put a bit of shade over them. They should recover OK.
I have a full page about it here;
.TOMATO AND CUCUMBER LEAF SCORCH